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Chapter 21 (Part 2). Transcriptional Regulation and RNA Processing. Regulation of Gene Expression. RNA Processing. mRNA. RNA Degradation. 5’CAP. AAAAAA. Active enzyme. Post-translational modification. Protein Degradation. Activators and Repressors. co-A. A. RNAP. +1. RNAP.
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Chapter 21 (Part 2) Transcriptional Regulation and RNA Processing
Regulation of Gene Expression RNA Processing mRNA RNA Degradation 5’CAP AAAAAA Active enzyme Post-translational modification Protein Degradation
Activators and Repressors co-A A RNAP +1 RNAP co-R R +1
The Helix-Turn-Helix Motif • contain two alpha helices separated by a loop with a beta turn • The C-terminal helix fits in major groove of DNA; N-terminal helix stabilizes by hydrophobic interactions with C-terminal helix
The Zn-Finger Motif Zn fingers form a folded beta strand and an alpha helix that fits into the DNA major groove.
The Leucine Zipper Motif • Forms amphipathic alpha helix and a coiled-coil dimer • Leucine zipper proteins dimerize, either as homo- or hetero-dimers • The basic region is the DNA-recognition site • Basic region is often modeled as a pair of helices that can wrap around the major groove
Binding of some trans-factors is regulated by allosteric modification
Glucose is E. coli’s primary carbon source. But.. it can grow on different carbon sources.
Diauxic growth of E. coli on a mixture of lactose + glucose.
Inhibition of repression of lac operon by inducer binding to lacI
Inducer : Allolactose, produced by side reaction of lacZ Lehninger: Principles of Biochemistry, 3rd Ed.
IPTG is a Gratuitous Inducer • Synthetic molecule
Repression of the Tryptophan operon: A variation of the theme
Why does the Lac Operon need an activator? Lac promoter has lousy promoter!!!
