Transcriptional regulation in Bacteria Thanks to the relative ease of doing genetics with bacteria transcriptional regulation in bacteria is better understood than that in other organisms and has served as a framework for understanding transcriptional regulation in eukaryotic organisms There are important differences between the mechanisms of transcriptional regulation in bacteria and higher organisms, many of which relate to the presence of a nuclear membrane Nevertheless, many of the strategies used are similar throughout the biological world, and many general principles have been uncovered through studies of bacterial transcriptional regulation
• Transcriptional Regulation in Bacteria • Thanks to the relative ease of doing genetics with bacteria, transcriptional regulation in bacteria is better understood than that in other organisms and has served as a framework for understanding transcriptional regulation in eukaryotic organisms. There are important differences between the mechanisms of transcriptional regulation in bacteria and higher organisms, many of which relate to the presence of a nuclear membrane. Nevertheless, many of the strategies used are similar throughout the biological world, and many general principles have been uncovered through studies of bacterial transcriptional regulation
(A)The two general types of transcriptional regulation. In negative regulation, a repressor binds OFF to an operator and turns the operon off. In positive regulation,an activator protein binds upstream of the promoter and turns the operon on B)Graph showing the usual locations of activator sites relative to operators. Activator sites are usually farther upstream Each datum point Act valor sites indicates the middle of the known vo2a region on the dna where a regulatory protein binds LI 80-60-40-20 Base pairs coordinate
(A) The two general types of transcriptional regulation. In negative regulation, a repressor binds to an operator and turns the operon off. In positive regulation, an activator protein binds upstream of the promoter and turns the operon on. (B) Graph showing the usual locations of activator sites relative to operators. Activator sites are usually farther upstream. Each datum point indicates the middle of the known region on the DNA where a regulatory protein binds
The Bacterial Operon The concept of an operon is central to hypotheses about bacterial transcriptional regulation. Bacterial genes are often arranged so that more than one gene can be transcribed into the same polycistronic mRNA. In such cases. the genes are said to be cotranscribed. Cotranscription of more than one gene into a polycistronic mRNA Seems to be unique to bacteria and their phages and affects the types of translational initiation regions TIR)used on the mRNA. In eukaryotes, generally the first AUg codon in an mrNa is used to initiate translation so that only one polypeptide can be encoded by each mRNA However, bacterial TIRs are much more complex. Shine Dalgarno and other sequences help define the tir because of its distinct structure. a bacterial TIR will be recognized wherever it appears in the mRNA, and more than one tir can be recognized in the same mRNA
• The Bacterial Operon • The concept of an operon is central to hypotheses about bacterial transcriptional regulation. Bacterial genes are often arranged so that more than one gene can be transcribed into the same polycistronic mRNA. In such cases, the genes are said to be cotranscribed. Cotranscription of more than one gene into a polycistronic mRNA seems to be unique to bacteria and their phages and affects the types of translational initiation regions (TIR) used on the mRNA. In eukaryotes, generally the first AUG codon in an mRNA is used to initiate translation so that only one polypeptide can be encoded by each mRNA. However, bacterial TIRs are much more complex. ShineDalgarno and other sequences help define the TIR. Because of its distinct structure, a bacterial TIR will be recognized wherever it appears in the mRNA, and more than one TIR can be recognized in the same mRNA
a bacterial operon is the region on the dna that includes genes cotranscribed into the same mRNa plus all of the adjacent cis-acting sequences required for transcription of these genes, including the genes' promoter as well as operators and other sequences involved in regulating the transcription of the genes. Because the genes of an operon are all transcribed from the same promoter and use the same regulatory sequences, all the genes of an operon can be transcriptionally regulated simultaneously
• A bacterial operon is the region on the DNA that includes genes cotranscribed into the same mRNA plus all of the adjacent cis-acting sequences required for transcription of these genes, including the genes' promoter as well as operators and other sequences involved in regulating the transcription of the genes. Because the genes of an operon are all transcribed from the same promoter and use the same regulatory sequences, all the genes of an operon can be transcriptionally regulated simultaneously
Repressors and Activators Before discussing our examples of transcriptional regulation in bacteria, we give a brief overview of the types of regulation known to occur and define some of the terms that describe the factors involved. The transcription of bacterial operons is regulated by the products of regulatory genes, which are often proteins called repressors or activators. These regulatory proteins bind close to the operon,s promoter and regulate transcription from the promoter. Sometimes, a regulatory protein can play dual roles and can also perform an enzymatic reaction in the pathway encoded by the operon Because they bind to DNA. repressors and activators often have the helix-turn-helix motif shared by many dna binding proteins Repressors bind to sites called operators and turn off the promoter, thereby preventing transcription of the genes of the operon. Activators, in contrast, bind to activator sites and turn on the promoter, thereby facilitating transcription of the operon genes
• Repressors and Activators • Before discussing our examples of transcriptional regulation in bacteria, we give a brief overview of the types of regulation known to occur and define some of the terms that describe the factors involved. The transcription of bacterial operons is regulated by the products of regulatory genes, which are often proteins called repressors or activators. These regulatory proteins bind close to the operon's promoter and regulate transcription from the promoter. Sometimes, a regulatory protein can play dual roles and can also perform an enzymatic reaction in the pathway encoded by the operon. Because they bind to DNA, repressors and activators often have the helix-turn-helix motif shared by many DNA binding proteins . • Repressors bind to sites called operators and turn off the promoter, thereby preventing transcription of the genes of the operon. Activators, in contrast, bind to activator sites and turn on the promoter, thereby facilitating transcription of the operon genes