Chapter 21 (Part 2)

1
Chapter 21 (Part 2)

• Transcriptional Regulation and
• RNA Processing

2
Regulation of Gene Expression
RNA Processing
mRNA
RNA Degradation
AAAAAA
5CAP
Active enzyme
Post-translational modification
Protein Degradation
3
(No Transcript)
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. colis 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

18
(No Transcript)
19
(No Transcript)
20
Repression of the Tryptophan operon A variation
of the theme
21
Catabolite Repression of lac Operon (Positive
regulation)
22
(No Transcript)
23
Molecular Cell Biology, 4th Edition, Lodish et.
al. (2000)
24
(No Transcript)
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
29
(No Transcript)
30
(No Transcript)
31
Splicing of Pre-mRNA
32
Splicing of Pre-mRNA