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Chapter 16
Regulation in Prokaryotes
23 and 25 October, 2006
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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.
Activators and
repressors may
regulate binding
of polymerase.
Some activators regulate open complex formation.
Cooperative Binding and Transcriptional
Regulation at a Distance
The lac operon
lac operon regulation
Control Regions and lac Operator Half-sites
RNA
polymerase can
form open
complexes even
in the presence
of the LacI
protein.
RNA polymerase interacts with promoter and
CAP
Helix-turn-helix Interactions with DNA
CAP bends DNA
Activator
Bypass
Lac repressor binds as a tetramer
Genetic experiments with partial diploids elucidated
the ideas behind regulation of gene expression.
Regulation by Alternative s-Factors
Regulation of GlnA by s-54 and NtrC.
NtrC Acts at a Distance
MerR Regulation
AraC Regulation
Arabinose relaxes loops, and the loops reform
in the absence of competitor.
Regulation of the trp operon
Tryptophan Interaction with Trp Repressor
Attenuation
Ribosomal
proteins
regulate their
own
translation.
Riboswitches
regulate gene
expression
without
regulatory
proteins.
Phage
lambda
Lambda
Genome
Lambda Control Region
Lambda
Repressor and
Binding Sites
Cooperative
Binding
Cooperative and Non-Cooperative Binding
Lambda Regulation
Negative Autoregulation
DNA Looping Between two lac operators
CII Control of the Lytic / Lysogenic Decision
N and Q Antiterminators
int Regulation
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