Transcript The ATM repair pathway inhibits RNA polymerase I transcription in

•Homework #2 is posted and due 10/17
•Exams should be returned on W 10/3
Each step in gene
expression presents an
opportunity to regulate
when and how much of
a gene product will be
produced.
Why change gene
expression?
•Different cells need
different components
•Responding to the
environment
•Replacement of
damaged/worn-out parts
Two points to keep in
mind:
1. Cellular components
are constantly turnedover.
2. Gene expression takes
time:
Typically more than an
hour from DNA to
protein. Most
rapidly 15 minutes.
DNA damage inhibits rRNA transciption
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Fig 1a
The ATM repair pathway inhibits RNA polymerase I
transcription in response to chromosome breaks
Nature Vol 447 pg 730-734 (7 June 2007)
In bacteria, transcription and translation occur
simultaneously. So most regulation of gene
expression happens at transcription.
Fig 8.11
Transcription initiation in prokaryotes:
sigma factor binds to the -35 and -10 regions and then
the RNA polymerase subunits bind and begin
transcription
Fig 8.8
Operon: several genes
whose expression is
controlled by the same
promoter
Fig 10.4+.5
Fig 10.5
E. coli lactose metabolism
Fig 10.6
In the absence of lactose, the lac operon is
repressed.
Fig 10.6
Lactose binds to the repressor, making it
inactive, so that transcription can occur.
Fig 10.6
Glucose is a better energy source
than lactose
Fig 10.13
Low glucose leads to high cAMP
cAMP binds to CAP
which increases lac
operon transcription
Fig 10.13
High glucose leads to
low cAMP
low cAMP, CAP inactive, low
lac operon transcription
Fig 10.13
The lac operon: one
example of regulating
gene expression in
bacteria
Fig 10.4+.5