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Unformatted text preview: Figure 08-48 Figure 7-69 Molecular Biology of the Cell (© Garland Science 2008) Figure 7-67 Molecular Biology of the Cell (© Garland Science 2008) Figure 08-48 T82T84G78A65C54A45 T80A95T45A60A50T96 Initial binding is a reversible reaction defined by equilibrium constant
KB =[closed complex]/ [free DNA] [free RNAP] How do activators work?
Lac promoter does not match consensus
TT G A C A TATAAT GCGCAA CATGAT Lac promoter seq. Hypothesis: CAP and RNAP physically interact and
thus bind cooperatively to their sites What testable predictions are implicit in such a hypothesis? • CAP & RNAP should bind together w/ higher affinity than
either alone (cooperativity).
• mutations that alter region of interaction should affect DNA
• 2 proteins should interact in vitro
• CAP should affect KB, not k2
• If you make the RNAP binding site a high affinity site,
transcription should be independent of CAP Five principles of gene regulation:
I. Level of gene expression set by promoter sequence T82T84G78A65C54A45 T80A95T45A60A50T96 The afﬁnity of RNAP for promoter is set by the -35 sequence=KB
The rate of open complex formation is set by -10 sequence=k2 II. Transcription is regulated by sequence-specific
DNA-binding proteins Laci promoter is
constitutive and weak Mutations in genes for such regulatory proteins are pleiotropic
Mutations in the binding site are pleiotropic, but in cis III. Regulatory proteins can function as activators or repressors inducible
repressible repressible inducible Ligand binding can either activate or inactivate DNA-binding inducible
repressible repressible inducible inducible
repressible repressible inducible Molecular mechanism of repression/activation can vary KB Repressor can block RNAP binding
Activator can increase RNAP binding Closed complex k2 Repressor can block open complex
Activator can facilitate open complex Open complex Abortive initiation Repressor can block promoter clearance Protein:protein interactions double the number of contacts between the protein and DNA and
increase the afﬁnity of the protein for the site. V. Combinatorial Regulation: Regulatory DNA sequences that
bind 2 control proteins can integrate two signals to give a
single output You could accomplish same outcome by having multiple repressors that must all be
removed, or multiple activators that must all be present for transcription ...
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This note was uploaded on 12/05/2011 for the course BIO 344 taught by Professor Herrin during the Spring '08 term at University of Texas at Austin.
- Spring '08
- molecular biology