{"id":1025,"date":"2022-04-20T21:11:39","date_gmt":"2022-04-20T21:11:39","guid":{"rendered":"https:\/\/pressbooks.hcfl.edu\/bio1\/chapter\/prokaryotic-gene-regulation\/"},"modified":"2025-08-29T19:17:22","modified_gmt":"2025-08-29T19:17:22","slug":"prokaryotic-gene-regulation","status":"publish","type":"chapter","link":"https:\/\/pressbooks.hcfl.edu\/bio1\/chapter\/prokaryotic-gene-regulation\/","title":{"raw":"Prokaryotic Gene Regulation","rendered":"Prokaryotic Gene Regulation"},"content":{"raw":"<div class=\"textbox textbox--learning-objectives\"><header class=\"textbox__header\">\n<h2 class=\"textbox__title\">Learning Objectives<\/h2>\n<\/header>\n<div class=\"textbox__content\">\n\nBy the end of this section, you will be able to do the following:\n<ul>\n \t<li>Describe the steps involved in prokaryotic gene regulation<\/li>\n \t<li>Explain the roles of activators, inducers, and repressors in gene regulation<\/li>\n<\/ul>\n<\/div>\n<\/div>\nThe DNA of prokaryotes is organized into a circular chromosome, supercoiled within the nucleoid region of the cell cytoplasm. Proteins that are needed for a specific function, or that are involved in the same biochemical pathway, are encoded together in blocks called\u00a0<strong><span id=\"term600\" data-type=\"term\">operons<\/span><\/strong>. For example, all of the genes needed to use lactose as an energy source are coded next to each other in the lactose (or\u00a0<em data-effect=\"italics\">lac<\/em>) operon, and transcribed into a single mRNA.\n\nIn prokaryotic cells, there are three types of regulatory molecules that can affect the expression of operons: repressors, activators, and inducers. Repressors and activators are proteins produced in the cell. Both repressors and activators regulate gene expression by binding to specific DNA sites\u00a0<em data-effect=\"italics\">adjacent<\/em>\u00a0to the genes they control.\u00a0<em data-effect=\"italics\">In general, activators bind to the promoter site, while repressors bind to operator regions<\/em>.\u00a0<strong><span id=\"term601\" data-type=\"term\">Repressors<\/span>\u00a0<\/strong>prevent transcription of a gene in response to an external stimulus, whereas\u00a0<strong><span id=\"term602\" data-type=\"term\">activators<\/span>\u00a0<\/strong>increase the transcription of a gene in response to an external stimulus. Inducers are small molecules that may be produced by the cell or that are in the cell\u2019s environment. Inducers either activate or repress transcription depending on the needs of the cell and the availability of substrate.\n\n<section id=\"fs-idm82649424\" data-depth=\"1\">\n<h3 data-type=\"title\">The\u00a0<em data-effect=\"italics\">trp<\/em>\u00a0Operon: A Repressible Operon<\/h3>\n<p id=\"fs-idm166815232\">Bacteria such as\u00a0<em data-effect=\"italics\">Escherichia coli<\/em>\u00a0need amino acids to survive, and are able to synthesize many of them.\u00a0<strong><span id=\"term603\" data-type=\"term\">Tryptophan<\/span>\u00a0<\/strong>is one such amino acid that\u00a0<em data-effect=\"italics\">E. coli<\/em>\u00a0can either ingest from the environment or synthesize using enzymes that are encoded by five genes. These five genes are next to each other in what is called the\u00a0<strong><span id=\"term604\" data-type=\"term\">tryptophan (<em data-effect=\"italics\">trp<\/em>) operon<\/span>\u00a0<\/strong>(Figure 16.4). The genes are transcribed into a single mRNA, which is then translated to produce all five enzymes. If tryptophan is present in the environment, then\u00a0<em data-effect=\"italics\">E. coli<\/em>\u00a0does not need to synthesize it and the\u00a0<em data-effect=\"italics\">trp<\/em>\u00a0operon is switched off. However, when tryptophan availability is low, the switch controlling the operon is turned on, the mRNA is transcribed, the enzyme proteins are translated, and tryptophan is synthesized.<\/p>\n\n<div id=\"fig-ch16_02_01\" class=\"os-figure\">\n<figure data-id=\"fig-ch16_02_01\"><span id=\"fs-idm229109280\" data-type=\"media\" data-alt=\"The t r p operon has a promoter, an operator, and five genes named t r p upper case E; t r p upper case D, t r p upper case C, t r p upper case B, and t r p upper case A that are located in sequential order on the D N A. R N A polymerase binds to the promoter. When tryptophan is present, the t r p repressor binds the operator and prevents the R N A polymerase from moving past the operator; therefore, R N A synthesis is blocked. In the absence of tryptophan, the repressor dissociates from the operator. R N A polymerase can now slide past the operator, and transcription begins.\"><\/span><\/figure>\n<div class=\"os-caption-container\"><span class=\"os-caption\">\u00a0<\/span><\/div>\n<div>\n\n[caption id=\"attachment_1022\" align=\"aligncenter\" width=\"800\"]<img class=\"wp-image-1022 size-full\" src=\"http:\/\/pressbooks.hcfl.edu\/bio1\/wp-content\/uploads\/sites\/106\/2022\/04\/General-Biology-I-Lecture-Lab-1657046460_Page_753_Image_0001.jpg\" alt=\"The t r p operon has a promoter, an operator, and five genes named t r p upper case E; t r p upper case D, t r p upper case C, t r p upper case B, and t r p upper case A that are located in sequential order on the D N A. R N A polymerase binds to the promoter. When tryptophan is present, the t r p repressor binds the operator and prevents the R N A polymerase from moving past the operator; therefore, R N A synthesis is blocked. In the absence of tryptophan, the repressor dissociates from the operator. R N A polymerase can now slide past the operator, and transcription begins.\" width=\"800\" height=\"523\"> Figure\u00a016.4\u00a0The tryptophan operon. The five genes that are needed to synthesize tryptophan in\u00a0E. coli\u00a0are located next to each other in the\u00a0trp\u00a0operon. When tryptophan is plentiful, two tryptophan molecules bind the repressor protein at the operator sequence. This physically blocks the RNA polymerase from transcribing the tryptophan genes. When tryptophan is absent, the repressor protein does not bind to the operator and the genes are transcribed.[\/caption]\n\n<\/div>\n<\/div>\n<p id=\"fs-idm174533984\">The\u00a0<em data-effect=\"italics\">trp<\/em>\u00a0operon includes three important regions: the coding region, the\u00a0<em data-effect=\"italics\">trp<\/em>\u00a0operator and the\u00a0<em data-effect=\"italics\">trp<\/em>\u00a0promoter. The coding region includes the genes for the five tryptophan biosynthesis enzymes. Just before the coding region is the\u00a0<span id=\"term605\" data-type=\"term\"><strong>transcriptional start site<\/strong><\/span>. The promoter sequence, to which RNA polymerase binds to initiate transcription, is before or \u201cupstream\u201d of the transcriptional start site. Between the promoter and the transcriptional start site is the operator region.<\/p>\n<p id=\"fs-idm199850336\">The\u00a0<em data-effect=\"italics\">trp<\/em>\u00a0<strong><span id=\"term606\" data-type=\"term\">operator<\/span>\u00a0<\/strong>contains the DNA code to which the\u00a0<em data-effect=\"italics\">trp<\/em>\u00a0repressor protein can bind. However, the repressor alone cannot bind to the operator. When tryptophan is present in the cell, two tryptophan molecules bind to the\u00a0<em data-effect=\"italics\">trp<\/em>\u00a0repressor, which changes the shape of the repressor protein to a form that can bind to the\u00a0<em data-effect=\"italics\">trp<\/em>\u00a0operator. Binding of the tryptophan\u2013repressor complex at the operator physically prevents the RNA polymerase from binding to the promoter and transcribing the downstream genes.<\/p>\n<p id=\"fs-idm101642592\">When tryptophan is not present in the cell, the repressor by itself does not bind to the operator, the polymerase can transcribe the enzyme genes, and tryptophan is synthesized. Because the repressor protein actively binds to the operator to keep the genes turned off, the\u00a0<em data-effect=\"italics\">trp<\/em>\u00a0operon is said to be\u00a0<em data-effect=\"italics\">negatively regulated<\/em>\u00a0and the proteins that bind to the operator to silence\u00a0<em data-effect=\"italics\">trp<\/em>\u00a0expression are<strong>\u00a0<span id=\"term607\" data-type=\"term\">negative regulators<\/span><\/strong>.<\/p>\n\n<div class=\"textbox\">\n<h4 id=\"3\" class=\"os-subtitle\" data-type=\"title\"><span class=\"os-subtitle-label\">Link to Learning<\/span><\/h4>\n<p id=\"fs-idm19622064\">Watch this video to learn more about the\u00a0<em data-effect=\"italics\">trp<\/em>\u00a0operon.<\/p>\n\n<div id=\"eip-id1169842033659\" data-type=\"media\" data-alt=\"trp_operon\">\n<div class=\"os-has-iframe os-has-link\" data-type=\"alternatives\"><a class=\"os-is-link\" href=\"https:\/\/www.openstax.org\/l\/trp_operon\" target=\"_blank\" rel=\"noopener nofollow\">Click to view content<\/a><\/div>\n<\/div>\n<\/div>\n<h3 data-type=\"title\">Catabolite Activator Protein (CAP): A Transcriptional Activator<\/h3>\n<span style=\"font-size: 1em\">Just as the\u00a0<\/span><em style=\"font-size: 1em\" data-effect=\"italics\">trp<\/em><span style=\"font-size: 1em\">\u00a0operon is negatively regulated by tryptophan molecules, there are proteins that bind to the promoter sequences that act as\u00a0<\/span><strong><span id=\"term608\" style=\"font-size: 1em\" data-type=\"term\">positive regulators<\/span><\/strong><span style=\"font-size: 1em\">\u00a0to turn genes on and activate them. For example, when glucose is scarce,\u00a0<\/span><em style=\"font-size: 1em\" data-effect=\"italics\">E. coli<\/em><span style=\"font-size: 1em\">\u00a0bacteria can turn to other sugar sources for fuel. To do this, new genes to process these alternate sugars must be transcribed. When glucose levels drop, cyclic AMP (cAMP) begins to accumulate in the cell. The cAMP molecule is a signaling molecule that is involved in glucose and energy metabolism in\u00a0<\/span><em style=\"font-size: 1em\" data-effect=\"italics\">E. coli<\/em><span style=\"font-size: 1em\">. Accumulating cAMP binds to the positive regulator\u00a0<\/span><strong><span id=\"term609\" style=\"font-size: 1em\" data-type=\"term\">catabolite activator protein (CAP)<\/span><\/strong><span style=\"font-size: 1em\">, a protein that binds to the promoters of operons which control the processing of alternative sugars. When cAMP binds to CAP, the complex then binds to the promoter region of the genes that are needed to use the alternate sugar sources (<\/span>Figure 16.5<span style=\"font-size: 1em\">). In these operons, a CAP-binding site is located upstream of the RNA-polymerase-binding site in the promoter. CAP binding stabilizes the binding of RNA polymerase to the promoter region and increases transcription of the associated protein-coding genes.<\/span>\n\n<\/section><section id=\"fs-idm202194608\" data-depth=\"1\">\n<div id=\"fig-ch16_02_02\" class=\"os-figure\">\n<figure data-id=\"fig-ch16_02_02\"><span id=\"fs-idm287484176\" data-type=\"media\" data-alt=\"The lac operon consists of a promoter, an operator, and three genes named lac Z, lac Y, and lac A that are located in sequential order on the D N A. In the absence of c A M P, the CAP protein does not bind the D N A. R N A polymerase binds the promoter, and transcription occurs at a slow rate. In the presence of c A M P, a CAP, c A M P complex binds to the promoter and increases R N A polymerase activity. As a result, the rate of R N A synthesis is increased.\"><\/span><\/figure>\n<div class=\"os-caption-container\"><span class=\"os-caption\">\u00a0<\/span><\/div>\n<div>\n\n[caption id=\"attachment_1023\" align=\"aligncenter\" width=\"800\"]<img class=\"wp-image-1023 size-full\" src=\"http:\/\/pressbooks.hcfl.edu\/bio1\/wp-content\/uploads\/sites\/106\/2025\/08\/General-Biology-I-Lecture-Lab-1657046460_Page_754_Image_0001.jpg\" alt=\"The lac operon consists of a promoter, an operator, and three genes named lac Z, lac Y, and lac A that are located in sequential order on the D N A. In the absence of c A M P, the CAP protein does not bind the D N A. R N A polymerase binds the promoter, and transcription occurs at a slow rate. In the presence of c A M P, a CAP, c A M P complex binds to the promoter and increases R N A polymerase activity. As a result, the rate of R N A synthesis is increased.\" width=\"800\" height=\"474\"> Figure\u00a016.5\u00a0Transcriptional activation by the CAP protein. When glucose levels fall,\u00a0E. coli\u00a0may use other sugars for fuel but must transcribe new genes to do so. As glucose supplies become limited, cAMP levels increase. This cAMP binds to the CAP protein, a positive regulator that binds to a promoter region upstream of the genes required to use other sugar sources.[\/caption]\n\n<\/div>\n<\/div>\n<\/section><section id=\"fs-idm146228272\" data-depth=\"1\">\n<h3 data-type=\"title\">The\u00a0<em data-effect=\"italics\">lac<\/em>\u00a0Operon: An Inducible Operon<\/h3>\n<p id=\"fs-idm17029296\">The third type of gene regulation in prokaryotic cells occurs through\u00a0<em data-effect=\"italics\">inducible operons<\/em>, which have proteins that bind to activate or repress transcription depending on the local environment and the needs of the cell. The\u00a0<em data-effect=\"italics\">lac<\/em>\u00a0operon is a typical inducible operon. As mentioned previously,\u00a0<em data-effect=\"italics\">E. coli<\/em>\u00a0is able to use other sugars as energy sources when glucose concentrations are low. One such sugar source is lactose. The\u00a0<span id=\"term610\" data-type=\"term\"><em data-effect=\"italics\">lac<\/em>\u00a0operon<\/span> encodes the genes necessary to acquire and process the lactose from the local environment. The Z gene of the\u00a0<strong><em data-effect=\"italics\">lac<\/em>\u00a0operon<\/strong> encodes beta-galactosidase, which breaks lactose down to glucose and galactose.<\/p>\nHowever, for the\u00a0<em data-effect=\"italics\">lac<\/em>\u00a0operon to be activated, two conditions must be met. First, the level of glucose must be very low or non-existent. Second, lactose must be present. Only when glucose is absent and lactose is present will the\u00a0<em data-effect=\"italics\">lac<\/em>\u00a0operon be transcribed (Figure 16.6). In the absence of glucose, the binding of the CAP protein makes transcription of the\u00a0<em data-effect=\"italics\">lac<\/em>\u00a0operon more effective. When lactose is present, its metabolite, allolactose, binds to the\u00a0<em data-effect=\"italics\">lac<\/em>\u00a0repressor and changes its shape so that it cannot bind to the\u00a0<em data-effect=\"italics\">lac<\/em> operator to prevent transcription. This combination of conditions makes sense for the cell, because it would be energetically wasteful to synthesize the enzymes to process lactose if glucose was plentiful or lactose was not available. It should be mentioned that the lac operon is transcribed at a very low rate even when glucose is present and lactose absent.\n<div class=\"textbox\">\n<h4 id=\"5\" class=\"os-subtitle\" data-type=\"title\"><span class=\"os-subtitle-label\">Visual Connection<\/span><\/h4>\n<div id=\"fig-ch16_02_03\" class=\"os-figure\">\n<figure data-id=\"fig-ch16_02_03\"><span id=\"fs-idm178409184\" data-type=\"media\" data-alt=\"The lac operon consists of a promoter, an operator, and three genes named lac Z, lac Y, and lac A. R N A polymerase binds to the promoter. In the absence of lactose, the lac repressor binds to the operator and prevents RNA polymerase from transcribing the operon. In the presence of lactose, the repressor is released from the operator, and transcription proceeds at a slow rate. Binding of the c A M P plus sign CAP complex to the promoter stimulates R N A polymerase activity and increases R N A synthesis. However, even in the presence of the c A M P plus sign CAP complex, R N A synthesis is blocked if the repressor binds to the promoter.\"><\/span><\/figure>\n<div class=\"os-caption-container\"><span class=\"os-caption\">\u00a0<\/span><\/div>\n<div>\n\n[caption id=\"attachment_1024\" align=\"aligncenter\" width=\"469\"]<img class=\"wp-image-1024 size-full\" src=\"http:\/\/pressbooks.hcfl.edu\/bio1\/wp-content\/uploads\/sites\/106\/2025\/08\/85.png\" alt=\"The lac operon consists of a promoter, an operator, and three genes named lac Z, lac Y, and lac A. R N A polymerase binds to the promoter. In the absence of lactose, the lac repressor binds to the operator and prevents RNA polymerase from transcribing the operon. In the presence of lactose, the repressor is released from the operator, and transcription proceeds at a slow rate. Binding of the c A M P plus sign CAP complex to the promoter stimulates R N A polymerase activity and increases R N A synthesis. However, even in the presence of the c A M P plus sign CAP complex, R N A synthesis is blocked if the repressor binds to the promoter.\" width=\"469\" height=\"829\"> Figure\u00a016.6\u00a0Regulation of the\u00a0lac\u00a0operon. Transcription of the\u00a0lac operon is carefully regulated so that its expression only occurs when glucose is limited and lactose is present to serve as an alternative fuel source.[\/caption]\n\n<\/div>\n<div><\/div>\n<div class=\"os-caption-container\"><span style=\"font-size: 1rem\">In\u00a0<\/span><em style=\"font-size: 1rem\" data-effect=\"italics\">E. coli<\/em><span style=\"font-size: 1rem\">, the\u00a0<\/span><em style=\"font-size: 1rem\" data-effect=\"italics\">trp<\/em><span style=\"font-size: 1rem\">\u00a0operon is on by default, while the\u00a0<\/span><em style=\"font-size: 1rem\" data-effect=\"italics\">lac<\/em><span style=\"font-size: 1rem\">\u00a0operon is off. Why do you think this is the case?<\/span><\/div>\n<\/div>\n<\/div>\n<span style=\"font-size: 1em\">If <\/span><span style=\"font-size: 1em\">glucose is present, then CAP fails to bind to the promoter sequence to activate transcription. If lactose is absent, then the repressor binds to the operator to prevent transcription. If either of these conditions is met, then transcription remains off. Only when glucose is absent and lactose is present is the <\/span><em style=\"font-size: 1em\" data-effect=\"italics\">lac<\/em><span style=\"font-size: 1em\">\u00a0operon transcribed (<\/span>Table 16.2<span style=\"font-size: 1em\">).<\/span>\n\n<\/section><section data-depth=\"1\"><\/section>\n<p style=\"text-align: center\" data-depth=\"1\"><strong>Signals that Induce or Repress Transcription of the\u00a0<em data-effect=\"italics\">lac<\/em>\u00a0Operon<\/strong><\/p>\n\n<table id=\"tab-ch16_02_01\" class=\"top-titled aligncenter\">\n<thead>\n<tr>\n<th scope=\"col\" data-align=\"center\">Glucose<\/th>\n<th scope=\"col\" data-align=\"center\">CAP binds<\/th>\n<th scope=\"col\" data-align=\"center\">Lactose<\/th>\n<th scope=\"col\" data-align=\"center\">Repressor binds<\/th>\n<th scope=\"col\" data-align=\"center\">Transcription<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td data-align=\"center\">+<\/td>\n<td data-align=\"center\">-<\/td>\n<td data-align=\"center\">-<\/td>\n<td data-align=\"center\">+<\/td>\n<td data-align=\"center\">No<\/td>\n<\/tr>\n<tr>\n<td data-align=\"center\">+<\/td>\n<td data-align=\"center\">-<\/td>\n<td data-align=\"center\">+<\/td>\n<td data-align=\"center\">-<\/td>\n<td data-align=\"center\">Some<\/td>\n<\/tr>\n<tr>\n<td data-align=\"center\">-<\/td>\n<td data-align=\"center\">+<\/td>\n<td data-align=\"center\">-<\/td>\n<td data-align=\"center\">+<\/td>\n<td data-align=\"center\">No<\/td>\n<\/tr>\n<tr>\n<td data-align=\"center\">-<\/td>\n<td data-align=\"center\">+<\/td>\n<td data-align=\"center\">+<\/td>\n<td data-align=\"center\">-<\/td>\n<td data-align=\"center\">Yes<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<div class=\"os-caption-container\" style=\"text-align: center\"><span class=\"os-title-label\">Table<\/span>\u00a0<span class=\"os-number\">16.2<\/span><\/div>\n<div>\n<div class=\"textbox\">\n<h4 id=\"7\" class=\"os-subtitle\" data-type=\"title\"><span class=\"os-subtitle-label\">Link to Learning<\/span><\/h4>\n<p id=\"fs-idm187859568\">Watch an animated tutorial about the workings of\u00a0<em data-effect=\"italics\">lac<\/em>\u00a0operon here.<\/p>\n\n<div id=\"eip-id1165239273914\" data-type=\"media\" data-alt=\"lac_operon\">\n<div class=\"os-has-iframe os-has-link\" data-type=\"alternatives\"><a class=\"os-is-link\" href=\"https:\/\/www.openstax.org\/l\/lac_operon\" target=\"_blank\" rel=\"noopener nofollow\">Click to view content<\/a><\/div>\n<\/div>\n<\/div>\n<\/div>","rendered":"<div class=\"textbox textbox--learning-objectives\">\n<header class=\"textbox__header\">\n<h2 class=\"textbox__title\">Learning Objectives<\/h2>\n<\/header>\n<div class=\"textbox__content\">\n<p>By the end of this section, you will be able to do the following:<\/p>\n<ul>\n<li>Describe the steps involved in prokaryotic gene regulation<\/li>\n<li>Explain the roles of activators, inducers, and repressors in gene regulation<\/li>\n<\/ul>\n<\/div>\n<\/div>\n<p>The DNA of prokaryotes is organized into a circular chromosome, supercoiled within the nucleoid region of the cell cytoplasm. Proteins that are needed for a specific function, or that are involved in the same biochemical pathway, are encoded together in blocks called\u00a0<strong><span id=\"term600\" data-type=\"term\">operons<\/span><\/strong>. For example, all of the genes needed to use lactose as an energy source are coded next to each other in the lactose (or\u00a0<em data-effect=\"italics\">lac<\/em>) operon, and transcribed into a single mRNA.<\/p>\n<p>In prokaryotic cells, there are three types of regulatory molecules that can affect the expression of operons: repressors, activators, and inducers. Repressors and activators are proteins produced in the cell. Both repressors and activators regulate gene expression by binding to specific DNA sites\u00a0<em data-effect=\"italics\">adjacent<\/em>\u00a0to the genes they control.\u00a0<em data-effect=\"italics\">In general, activators bind to the promoter site, while repressors bind to operator regions<\/em>.\u00a0<strong><span id=\"term601\" data-type=\"term\">Repressors<\/span>\u00a0<\/strong>prevent transcription of a gene in response to an external stimulus, whereas\u00a0<strong><span id=\"term602\" data-type=\"term\">activators<\/span>\u00a0<\/strong>increase the transcription of a gene in response to an external stimulus. Inducers are small molecules that may be produced by the cell or that are in the cell\u2019s environment. Inducers either activate or repress transcription depending on the needs of the cell and the availability of substrate.<\/p>\n<section id=\"fs-idm82649424\" data-depth=\"1\">\n<h3 data-type=\"title\">The\u00a0<em data-effect=\"italics\">trp<\/em>\u00a0Operon: A Repressible Operon<\/h3>\n<p id=\"fs-idm166815232\">Bacteria such as\u00a0<em data-effect=\"italics\">Escherichia coli<\/em>\u00a0need amino acids to survive, and are able to synthesize many of them.\u00a0<strong><span id=\"term603\" data-type=\"term\">Tryptophan<\/span>\u00a0<\/strong>is one such amino acid that\u00a0<em data-effect=\"italics\">E. coli<\/em>\u00a0can either ingest from the environment or synthesize using enzymes that are encoded by five genes. These five genes are next to each other in what is called the\u00a0<strong><span id=\"term604\" data-type=\"term\">tryptophan (<em data-effect=\"italics\">trp<\/em>) operon<\/span>\u00a0<\/strong>(Figure 16.4). The genes are transcribed into a single mRNA, which is then translated to produce all five enzymes. If tryptophan is present in the environment, then\u00a0<em data-effect=\"italics\">E. coli<\/em>\u00a0does not need to synthesize it and the\u00a0<em data-effect=\"italics\">trp<\/em>\u00a0operon is switched off. However, when tryptophan availability is low, the switch controlling the operon is turned on, the mRNA is transcribed, the enzyme proteins are translated, and tryptophan is synthesized.<\/p>\n<div id=\"fig-ch16_02_01\" class=\"os-figure\">\n<figure data-id=\"fig-ch16_02_01\"><span id=\"fs-idm229109280\" data-type=\"media\" data-alt=\"The t r p operon has a promoter, an operator, and five genes named t r p upper case E; t r p upper case D, t r p upper case C, t r p upper case B, and t r p upper case A that are located in sequential order on the D N A. R N A polymerase binds to the promoter. When tryptophan is present, the t r p repressor binds the operator and prevents the R N A polymerase from moving past the operator; therefore, R N A synthesis is blocked. In the absence of tryptophan, the repressor dissociates from the operator. R N A polymerase can now slide past the operator, and transcription begins.\"><\/span><\/figure>\n<div class=\"os-caption-container\"><span class=\"os-caption\">\u00a0<\/span><\/div>\n<div>\n<figure id=\"attachment_1022\" aria-describedby=\"caption-attachment-1022\" style=\"width: 800px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-1022 size-full\" src=\"http:\/\/pressbooks.hcfl.edu\/bio1\/wp-content\/uploads\/sites\/106\/2022\/04\/General-Biology-I-Lecture-Lab-1657046460_Page_753_Image_0001.jpg\" alt=\"The t r p operon has a promoter, an operator, and five genes named t r p upper case E; t r p upper case D, t r p upper case C, t r p upper case B, and t r p upper case A that are located in sequential order on the D N A. R N A polymerase binds to the promoter. When tryptophan is present, the t r p repressor binds the operator and prevents the R N A polymerase from moving past the operator; therefore, R N A synthesis is blocked. In the absence of tryptophan, the repressor dissociates from the operator. R N A polymerase can now slide past the operator, and transcription begins.\" width=\"800\" height=\"523\" srcset=\"https:\/\/pressbooks.hcfl.edu\/bio1\/wp-content\/uploads\/sites\/106\/2022\/04\/General-Biology-I-Lecture-Lab-1657046460_Page_753_Image_0001.jpg 800w, https:\/\/pressbooks.hcfl.edu\/bio1\/wp-content\/uploads\/sites\/106\/2022\/04\/General-Biology-I-Lecture-Lab-1657046460_Page_753_Image_0001-300x196.jpg 300w, https:\/\/pressbooks.hcfl.edu\/bio1\/wp-content\/uploads\/sites\/106\/2022\/04\/General-Biology-I-Lecture-Lab-1657046460_Page_753_Image_0001-768x502.jpg 768w, https:\/\/pressbooks.hcfl.edu\/bio1\/wp-content\/uploads\/sites\/106\/2022\/04\/General-Biology-I-Lecture-Lab-1657046460_Page_753_Image_0001-65x42.jpg 65w, https:\/\/pressbooks.hcfl.edu\/bio1\/wp-content\/uploads\/sites\/106\/2022\/04\/General-Biology-I-Lecture-Lab-1657046460_Page_753_Image_0001-225x147.jpg 225w, https:\/\/pressbooks.hcfl.edu\/bio1\/wp-content\/uploads\/sites\/106\/2022\/04\/General-Biology-I-Lecture-Lab-1657046460_Page_753_Image_0001-350x229.jpg 350w\" sizes=\"auto, (max-width: 800px) 100vw, 800px\" \/><figcaption id=\"caption-attachment-1022\" class=\"wp-caption-text\">Figure\u00a016.4\u00a0The tryptophan operon. The five genes that are needed to synthesize tryptophan in\u00a0E. coli\u00a0are located next to each other in the\u00a0trp\u00a0operon. When tryptophan is plentiful, two tryptophan molecules bind the repressor protein at the operator sequence. This physically blocks the RNA polymerase from transcribing the tryptophan genes. When tryptophan is absent, the repressor protein does not bind to the operator and the genes are transcribed.<\/figcaption><\/figure>\n<\/div>\n<\/div>\n<p id=\"fs-idm174533984\">The\u00a0<em data-effect=\"italics\">trp<\/em>\u00a0operon includes three important regions: the coding region, the\u00a0<em data-effect=\"italics\">trp<\/em>\u00a0operator and the\u00a0<em data-effect=\"italics\">trp<\/em>\u00a0promoter. The coding region includes the genes for the five tryptophan biosynthesis enzymes. Just before the coding region is the\u00a0<span id=\"term605\" data-type=\"term\"><strong>transcriptional start site<\/strong><\/span>. The promoter sequence, to which RNA polymerase binds to initiate transcription, is before or \u201cupstream\u201d of the transcriptional start site. Between the promoter and the transcriptional start site is the operator region.<\/p>\n<p id=\"fs-idm199850336\">The\u00a0<em data-effect=\"italics\">trp<\/em>\u00a0<strong><span id=\"term606\" data-type=\"term\">operator<\/span>\u00a0<\/strong>contains the DNA code to which the\u00a0<em data-effect=\"italics\">trp<\/em>\u00a0repressor protein can bind. However, the repressor alone cannot bind to the operator. When tryptophan is present in the cell, two tryptophan molecules bind to the\u00a0<em data-effect=\"italics\">trp<\/em>\u00a0repressor, which changes the shape of the repressor protein to a form that can bind to the\u00a0<em data-effect=\"italics\">trp<\/em>\u00a0operator. Binding of the tryptophan\u2013repressor complex at the operator physically prevents the RNA polymerase from binding to the promoter and transcribing the downstream genes.<\/p>\n<p id=\"fs-idm101642592\">When tryptophan is not present in the cell, the repressor by itself does not bind to the operator, the polymerase can transcribe the enzyme genes, and tryptophan is synthesized. Because the repressor protein actively binds to the operator to keep the genes turned off, the\u00a0<em data-effect=\"italics\">trp<\/em>\u00a0operon is said to be\u00a0<em data-effect=\"italics\">negatively regulated<\/em>\u00a0and the proteins that bind to the operator to silence\u00a0<em data-effect=\"italics\">trp<\/em>\u00a0expression are<strong>\u00a0<span id=\"term607\" data-type=\"term\">negative regulators<\/span><\/strong>.<\/p>\n<div class=\"textbox\">\n<h4 id=\"3\" class=\"os-subtitle\" data-type=\"title\"><span class=\"os-subtitle-label\">Link to Learning<\/span><\/h4>\n<p id=\"fs-idm19622064\">Watch this video to learn more about the\u00a0<em data-effect=\"italics\">trp<\/em>\u00a0operon.<\/p>\n<div id=\"eip-id1169842033659\" data-type=\"media\" data-alt=\"trp_operon\">\n<div class=\"os-has-iframe os-has-link\" data-type=\"alternatives\"><a class=\"os-is-link\" href=\"https:\/\/www.openstax.org\/l\/trp_operon\" target=\"_blank\" rel=\"noopener nofollow\">Click to view content<\/a><\/div>\n<\/div>\n<\/div>\n<h3 data-type=\"title\">Catabolite Activator Protein (CAP): A Transcriptional Activator<\/h3>\n<p><span style=\"font-size: 1em\">Just as the\u00a0<\/span><em style=\"font-size: 1em\" data-effect=\"italics\">trp<\/em><span style=\"font-size: 1em\">\u00a0operon is negatively regulated by tryptophan molecules, there are proteins that bind to the promoter sequences that act as\u00a0<\/span><strong><span id=\"term608\" style=\"font-size: 1em\" data-type=\"term\">positive regulators<\/span><\/strong><span style=\"font-size: 1em\">\u00a0to turn genes on and activate them. For example, when glucose is scarce,\u00a0<\/span><em style=\"font-size: 1em\" data-effect=\"italics\">E. coli<\/em><span style=\"font-size: 1em\">\u00a0bacteria can turn to other sugar sources for fuel. To do this, new genes to process these alternate sugars must be transcribed. When glucose levels drop, cyclic AMP (cAMP) begins to accumulate in the cell. The cAMP molecule is a signaling molecule that is involved in glucose and energy metabolism in\u00a0<\/span><em style=\"font-size: 1em\" data-effect=\"italics\">E. coli<\/em><span style=\"font-size: 1em\">. Accumulating cAMP binds to the positive regulator\u00a0<\/span><strong><span id=\"term609\" style=\"font-size: 1em\" data-type=\"term\">catabolite activator protein (CAP)<\/span><\/strong><span style=\"font-size: 1em\">, a protein that binds to the promoters of operons which control the processing of alternative sugars. When cAMP binds to CAP, the complex then binds to the promoter region of the genes that are needed to use the alternate sugar sources (<\/span>Figure 16.5<span style=\"font-size: 1em\">). In these operons, a CAP-binding site is located upstream of the RNA-polymerase-binding site in the promoter. CAP binding stabilizes the binding of RNA polymerase to the promoter region and increases transcription of the associated protein-coding genes.<\/span><\/p>\n<\/section>\n<section id=\"fs-idm202194608\" data-depth=\"1\">\n<div id=\"fig-ch16_02_02\" class=\"os-figure\">\n<figure data-id=\"fig-ch16_02_02\"><span id=\"fs-idm287484176\" data-type=\"media\" data-alt=\"The lac operon consists of a promoter, an operator, and three genes named lac Z, lac Y, and lac A that are located in sequential order on the D N A. In the absence of c A M P, the CAP protein does not bind the D N A. R N A polymerase binds the promoter, and transcription occurs at a slow rate. In the presence of c A M P, a CAP, c A M P complex binds to the promoter and increases R N A polymerase activity. As a result, the rate of R N A synthesis is increased.\"><\/span><\/figure>\n<div class=\"os-caption-container\"><span class=\"os-caption\">\u00a0<\/span><\/div>\n<div>\n<figure id=\"attachment_1023\" aria-describedby=\"caption-attachment-1023\" style=\"width: 800px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-1023 size-full\" src=\"http:\/\/pressbooks.hcfl.edu\/bio1\/wp-content\/uploads\/sites\/106\/2025\/08\/General-Biology-I-Lecture-Lab-1657046460_Page_754_Image_0001.jpg\" alt=\"The lac operon consists of a promoter, an operator, and three genes named lac Z, lac Y, and lac A that are located in sequential order on the D N A. In the absence of c A M P, the CAP protein does not bind the D N A. R N A polymerase binds the promoter, and transcription occurs at a slow rate. In the presence of c A M P, a CAP, c A M P complex binds to the promoter and increases R N A polymerase activity. As a result, the rate of R N A synthesis is increased.\" width=\"800\" height=\"474\" srcset=\"https:\/\/pressbooks.hcfl.edu\/bio1\/wp-content\/uploads\/sites\/106\/2025\/08\/General-Biology-I-Lecture-Lab-1657046460_Page_754_Image_0001.jpg 800w, https:\/\/pressbooks.hcfl.edu\/bio1\/wp-content\/uploads\/sites\/106\/2025\/08\/General-Biology-I-Lecture-Lab-1657046460_Page_754_Image_0001-300x178.jpg 300w, https:\/\/pressbooks.hcfl.edu\/bio1\/wp-content\/uploads\/sites\/106\/2025\/08\/General-Biology-I-Lecture-Lab-1657046460_Page_754_Image_0001-768x455.jpg 768w, https:\/\/pressbooks.hcfl.edu\/bio1\/wp-content\/uploads\/sites\/106\/2025\/08\/General-Biology-I-Lecture-Lab-1657046460_Page_754_Image_0001-65x39.jpg 65w, https:\/\/pressbooks.hcfl.edu\/bio1\/wp-content\/uploads\/sites\/106\/2025\/08\/General-Biology-I-Lecture-Lab-1657046460_Page_754_Image_0001-225x133.jpg 225w, https:\/\/pressbooks.hcfl.edu\/bio1\/wp-content\/uploads\/sites\/106\/2025\/08\/General-Biology-I-Lecture-Lab-1657046460_Page_754_Image_0001-350x207.jpg 350w\" sizes=\"auto, (max-width: 800px) 100vw, 800px\" \/><figcaption id=\"caption-attachment-1023\" class=\"wp-caption-text\">Figure\u00a016.5\u00a0Transcriptional activation by the CAP protein. When glucose levels fall,\u00a0E. coli\u00a0may use other sugars for fuel but must transcribe new genes to do so. As glucose supplies become limited, cAMP levels increase. This cAMP binds to the CAP protein, a positive regulator that binds to a promoter region upstream of the genes required to use other sugar sources.<\/figcaption><\/figure>\n<\/div>\n<\/div>\n<\/section>\n<section id=\"fs-idm146228272\" data-depth=\"1\">\n<h3 data-type=\"title\">The\u00a0<em data-effect=\"italics\">lac<\/em>\u00a0Operon: An Inducible Operon<\/h3>\n<p id=\"fs-idm17029296\">The third type of gene regulation in prokaryotic cells occurs through\u00a0<em data-effect=\"italics\">inducible operons<\/em>, which have proteins that bind to activate or repress transcription depending on the local environment and the needs of the cell. The\u00a0<em data-effect=\"italics\">lac<\/em>\u00a0operon is a typical inducible operon. As mentioned previously,\u00a0<em data-effect=\"italics\">E. coli<\/em>\u00a0is able to use other sugars as energy sources when glucose concentrations are low. One such sugar source is lactose. The\u00a0<span id=\"term610\" data-type=\"term\"><em data-effect=\"italics\">lac<\/em>\u00a0operon<\/span> encodes the genes necessary to acquire and process the lactose from the local environment. The Z gene of the\u00a0<strong><em data-effect=\"italics\">lac<\/em>\u00a0operon<\/strong> encodes beta-galactosidase, which breaks lactose down to glucose and galactose.<\/p>\n<p>However, for the\u00a0<em data-effect=\"italics\">lac<\/em>\u00a0operon to be activated, two conditions must be met. First, the level of glucose must be very low or non-existent. Second, lactose must be present. Only when glucose is absent and lactose is present will the\u00a0<em data-effect=\"italics\">lac<\/em>\u00a0operon be transcribed (Figure 16.6). In the absence of glucose, the binding of the CAP protein makes transcription of the\u00a0<em data-effect=\"italics\">lac<\/em>\u00a0operon more effective. When lactose is present, its metabolite, allolactose, binds to the\u00a0<em data-effect=\"italics\">lac<\/em>\u00a0repressor and changes its shape so that it cannot bind to the\u00a0<em data-effect=\"italics\">lac<\/em> operator to prevent transcription. This combination of conditions makes sense for the cell, because it would be energetically wasteful to synthesize the enzymes to process lactose if glucose was plentiful or lactose was not available. It should be mentioned that the lac operon is transcribed at a very low rate even when glucose is present and lactose absent.<\/p>\n<div class=\"textbox\">\n<h4 id=\"5\" class=\"os-subtitle\" data-type=\"title\"><span class=\"os-subtitle-label\">Visual Connection<\/span><\/h4>\n<div id=\"fig-ch16_02_03\" class=\"os-figure\">\n<figure data-id=\"fig-ch16_02_03\"><span id=\"fs-idm178409184\" data-type=\"media\" data-alt=\"The lac operon consists of a promoter, an operator, and three genes named lac Z, lac Y, and lac A. R N A polymerase binds to the promoter. In the absence of lactose, the lac repressor binds to the operator and prevents RNA polymerase from transcribing the operon. In the presence of lactose, the repressor is released from the operator, and transcription proceeds at a slow rate. Binding of the c A M P plus sign CAP complex to the promoter stimulates R N A polymerase activity and increases R N A synthesis. However, even in the presence of the c A M P plus sign CAP complex, R N A synthesis is blocked if the repressor binds to the promoter.\"><\/span><\/figure>\n<div class=\"os-caption-container\"><span class=\"os-caption\">\u00a0<\/span><\/div>\n<div>\n<figure id=\"attachment_1024\" aria-describedby=\"caption-attachment-1024\" style=\"width: 469px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-1024 size-full\" src=\"http:\/\/pressbooks.hcfl.edu\/bio1\/wp-content\/uploads\/sites\/106\/2025\/08\/85.png\" alt=\"The lac operon consists of a promoter, an operator, and three genes named lac Z, lac Y, and lac A. R N A polymerase binds to the promoter. In the absence of lactose, the lac repressor binds to the operator and prevents RNA polymerase from transcribing the operon. In the presence of lactose, the repressor is released from the operator, and transcription proceeds at a slow rate. Binding of the c A M P plus sign CAP complex to the promoter stimulates R N A polymerase activity and increases R N A synthesis. However, even in the presence of the c A M P plus sign CAP complex, R N A synthesis is blocked if the repressor binds to the promoter.\" width=\"469\" height=\"829\" srcset=\"https:\/\/pressbooks.hcfl.edu\/bio1\/wp-content\/uploads\/sites\/106\/2025\/08\/85.png 469w, https:\/\/pressbooks.hcfl.edu\/bio1\/wp-content\/uploads\/sites\/106\/2025\/08\/85-170x300.png 170w, https:\/\/pressbooks.hcfl.edu\/bio1\/wp-content\/uploads\/sites\/106\/2025\/08\/85-65x115.png 65w, https:\/\/pressbooks.hcfl.edu\/bio1\/wp-content\/uploads\/sites\/106\/2025\/08\/85-225x398.png 225w, https:\/\/pressbooks.hcfl.edu\/bio1\/wp-content\/uploads\/sites\/106\/2025\/08\/85-350x619.png 350w\" sizes=\"auto, (max-width: 469px) 100vw, 469px\" \/><figcaption id=\"caption-attachment-1024\" class=\"wp-caption-text\">Figure\u00a016.6\u00a0Regulation of the\u00a0lac\u00a0operon. Transcription of the\u00a0lac operon is carefully regulated so that its expression only occurs when glucose is limited and lactose is present to serve as an alternative fuel source.<\/figcaption><\/figure>\n<\/div>\n<div><\/div>\n<div class=\"os-caption-container\"><span style=\"font-size: 1rem\">In\u00a0<\/span><em style=\"font-size: 1rem\" data-effect=\"italics\">E. coli<\/em><span style=\"font-size: 1rem\">, the\u00a0<\/span><em style=\"font-size: 1rem\" data-effect=\"italics\">trp<\/em><span style=\"font-size: 1rem\">\u00a0operon is on by default, while the\u00a0<\/span><em style=\"font-size: 1rem\" data-effect=\"italics\">lac<\/em><span style=\"font-size: 1rem\">\u00a0operon is off. Why do you think this is the case?<\/span><\/div>\n<\/div>\n<\/div>\n<p><span style=\"font-size: 1em\">If <\/span><span style=\"font-size: 1em\">glucose is present, then CAP fails to bind to the promoter sequence to activate transcription. If lactose is absent, then the repressor binds to the operator to prevent transcription. If either of these conditions is met, then transcription remains off. Only when glucose is absent and lactose is present is the <\/span><em style=\"font-size: 1em\" data-effect=\"italics\">lac<\/em><span style=\"font-size: 1em\">\u00a0operon transcribed (<\/span>Table 16.2<span style=\"font-size: 1em\">).<\/span><\/p>\n<\/section>\n<section data-depth=\"1\"><\/section>\n<p style=\"text-align: center\" data-depth=\"1\"><strong>Signals that Induce or Repress Transcription of the\u00a0<em data-effect=\"italics\">lac<\/em>\u00a0Operon<\/strong><\/p>\n<table id=\"tab-ch16_02_01\" class=\"top-titled aligncenter\">\n<thead>\n<tr>\n<th scope=\"col\" data-align=\"center\">Glucose<\/th>\n<th scope=\"col\" data-align=\"center\">CAP binds<\/th>\n<th scope=\"col\" data-align=\"center\">Lactose<\/th>\n<th scope=\"col\" data-align=\"center\">Repressor binds<\/th>\n<th scope=\"col\" data-align=\"center\">Transcription<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td data-align=\"center\">+<\/td>\n<td data-align=\"center\">&#8211;<\/td>\n<td data-align=\"center\">&#8211;<\/td>\n<td data-align=\"center\">+<\/td>\n<td data-align=\"center\">No<\/td>\n<\/tr>\n<tr>\n<td data-align=\"center\">+<\/td>\n<td data-align=\"center\">&#8211;<\/td>\n<td data-align=\"center\">+<\/td>\n<td data-align=\"center\">&#8211;<\/td>\n<td data-align=\"center\">Some<\/td>\n<\/tr>\n<tr>\n<td data-align=\"center\">&#8211;<\/td>\n<td data-align=\"center\">+<\/td>\n<td data-align=\"center\">&#8211;<\/td>\n<td data-align=\"center\">+<\/td>\n<td data-align=\"center\">No<\/td>\n<\/tr>\n<tr>\n<td data-align=\"center\">&#8211;<\/td>\n<td data-align=\"center\">+<\/td>\n<td data-align=\"center\">+<\/td>\n<td data-align=\"center\">&#8211;<\/td>\n<td data-align=\"center\">Yes<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<div class=\"os-caption-container\" style=\"text-align: center\"><span class=\"os-title-label\">Table<\/span>\u00a0<span class=\"os-number\">16.2<\/span><\/div>\n<div>\n<div class=\"textbox\">\n<h4 id=\"7\" class=\"os-subtitle\" data-type=\"title\"><span class=\"os-subtitle-label\">Link to Learning<\/span><\/h4>\n<p id=\"fs-idm187859568\">Watch an animated tutorial about the workings of\u00a0<em data-effect=\"italics\">lac<\/em>\u00a0operon here.<\/p>\n<div id=\"eip-id1165239273914\" data-type=\"media\" data-alt=\"lac_operon\">\n<div class=\"os-has-iframe os-has-link\" data-type=\"alternatives\"><a class=\"os-is-link\" href=\"https:\/\/www.openstax.org\/l\/lac_operon\" target=\"_blank\" rel=\"noopener nofollow\">Click to view content<\/a><\/div>\n<\/div>\n<\/div>\n<\/div>\n","protected":false},"author":130,"menu_order":3,"template":"","meta":{"pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":["jung-choi","mary-ann-clark","matthew-douglas"],"pb_section_license":"cc-by"},"chapter-type":[],"contributor":[92,93,94],"license":[53],"class_list":["post-1025","chapter","type-chapter","status-publish","hentry","contributor-jung-choi","contributor-mary-ann-clark","contributor-matthew-douglas","license-cc-by"],"part":1013,"_links":{"self":[{"href":"https:\/\/pressbooks.hcfl.edu\/bio1\/wp-json\/pressbooks\/v2\/chapters\/1025","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/pressbooks.hcfl.edu\/bio1\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/pressbooks.hcfl.edu\/bio1\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/pressbooks.hcfl.edu\/bio1\/wp-json\/wp\/v2\/users\/130"}],"version-history":[{"count":1,"href":"https:\/\/pressbooks.hcfl.edu\/bio1\/wp-json\/pressbooks\/v2\/chapters\/1025\/revisions"}],"predecessor-version":[{"id":1026,"href":"https:\/\/pressbooks.hcfl.edu\/bio1\/wp-json\/pressbooks\/v2\/chapters\/1025\/revisions\/1026"}],"part":[{"href":"https:\/\/pressbooks.hcfl.edu\/bio1\/wp-json\/pressbooks\/v2\/parts\/1013"}],"metadata":[{"href":"https:\/\/pressbooks.hcfl.edu\/bio1\/wp-json\/pressbooks\/v2\/chapters\/1025\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/pressbooks.hcfl.edu\/bio1\/wp-json\/wp\/v2\/media?parent=1025"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/pressbooks.hcfl.edu\/bio1\/wp-json\/pressbooks\/v2\/chapter-type?post=1025"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/pressbooks.hcfl.edu\/bio1\/wp-json\/wp\/v2\/contributor?post=1025"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/pressbooks.hcfl.edu\/bio1\/wp-json\/wp\/v2\/license?post=1025"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}