1. Transcriptional Regulation and RNA Processing
Chapter 21 (Part 2)
Transcriptional Regulation and
RNA Processing

2. Regulation of Gene Expression
RNA Processing
mRNA
5’CAP
AAAAAA
RNA Degradation
Active
enzyme
Post-translational
modification
Protein Degradation

4. Activators and Repressors
co-A A
RNAP +1
RNAP
co-R R +1

5. 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

6. The Zn-Finger Motif
Zn fingers form a folded beta strand and an alpha helix that fits into the DNA major groove.

7. 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

8. Transcription Regulation in Prokaryotes

9. Binding of some trans-factors is regulated by allosteric modification

10. lac operon

11. Glucose is E. coli’s primary carbon source.
But.. it can grow on different carbon sources.

12. Diauxic growth of E. coli on a mixture of lactose + glucose.

13. The lac I protein

14. Operator and RNA Polymerase Bind at Overlapping Sites

15. Inhibition of repression of lac operon by inducer binding to lacI

16. Inducer : Allolactose, produced by side reaction of lacZ
Lehninger: Principles of Biochemistry, 3rd Ed.

17. IPTG is a Gratuitous Inducer
Synthetic molecule

20. Repression of the Tryptophan operon: A variation of the theme

21. Catabolite Repression of lac Operon (Positive regulation)

23. Molecular Cell Biology, 4th Edition, Lodish et. al. (2000)

25. Why does the Lac Operon need an activator?
Lac promoter has lousy promoter!!!

26. tRNA Processing

27. rRNA Processing

28. Processing of Eukaryotic mRNA

31. Splicing of Pre-mRNA

32. Splicing of Pre-mRNA