23 and 25 October, 2006 Chapter 16 Regulation in Prokaryotes.
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Transcript of 23 and 25 October, 2006 Chapter 16 Regulation in Prokaryotes.
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, binds 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.
Genetic experiments with partial diploids elucidated the ideas behind regulation of gene expression.