2. Transcriptional Regulation and
RNA Processing

3. RNA Processing
5’CAP
Active
enzyme
Post-translational
modification
mRNA
AAAAAA
RNA Degradation
Protein Degradation

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

6. 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

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

9. 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

12. Transcription Regulation in
Prokaryotes

14. lac operon

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

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

17. The lac I protein

18. Operator and RNA Polymerase Bind at
Overlapping Sites

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

21. Inducer :
Allolactose,
produced by side
reaction of lacZ

22. 
Synthetic molecule

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

26. Catabolite Repression of lac Operon
(Positive regulation)

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

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

36. Splicing of Pre-mRNA