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This chapter explores the intricate mechanisms of gene regulation in prokaryotes, focusing on transcriptional initiation as the primary regulatory point. Key processes include the binding of sequence-specific DNA-binding proteins, with a detailed analysis of the E. coli lac operon that showcases both repressors and activators. Techniques like DNA footprinting and mobility shift assays investigate macromolecular interactions. Various regulatory systems, riboswitches, and alternative regulatory strategies employed by phage lambda illustrate the complexity and diversity of prokaryotic gene regulation.
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Chapter 16 Regulation in Prokaryotes 25 and 27 October, 2004
Overview • Transcriptional initiation is the most common point to regulate gene expression. • Any of the events of initiation, including polymerase binding and open complex formation may be regulated either positively or negatively. • Regulation is accomplished by sequence-specific DNA binding proteins. • Binding may be promoter proximal or at a distance. • DNA footprinting and mobility shift assays are used to investigate the binding of regulatory proteins. • In the E. coli lac operon, there are both repressors and activators, each of which is allosterically regulated. • Many regulatory systems control a large number of genes and operons, like the catabolite repression and heat shock regulons. • NtrC is regulated by covalent modification, bidds at a distance, and hydrolyzes ATP to pronmote open complex formation. • MerR activates transcription by twisting the promoter. • Riboswitches regulate transcription or translation without protein mediators. • Phage lambda uses alternative regulatory systems to control lytic or lysogenic growth. • Repressor and Cro compete to determine lytic or lysogenic growth, in response to the stability of the CII protein. • Downstream regulation in lambda involves antitermination.
Activators and repressors may regulate binding of polymerase.
Cooperative Binding and Transcriptional Regulation at a Distance
RNA polymerase can form open complexes even in the presence of the LacI protein.
Genetic experiments with partial diploids elucidated the ideas behind regulation of gene expression.
Arabinose relaxes loops, and the loops reform in the absence of competitor.
Riboswitches regulate gene expression without regulatory proteins.
