11.14
Removal Figure of bulky lesions in DNA by UvrABC
Recombinational repair after the replisome encounters
a lesion on the leading strand template strand
Figure 11.15
Another model invokes fork regression to repair leading strand template damage
Figure 11.16
Cross-link removal by UvrABC
Figure 11.17
The SOS response to DNA damage
Figure 11.18
Reactions to DNA damage: the SOS response
The SOS response is a complex set of
physiological responses that are activated by
DNA damage in E. coli and many other, but not
all bacteria.
The responses result in higher cellular survival,
through the activation of pathways important for
both DNA and repair DNA damage tolerance
The SOS response is coordinated by the
multifunctional RecA protein and the LexA
transcriptional repressor
Inducing Signal= *RecA
RecA bound to singlestranded DNA in the
presence of nucleotide
triphosphate (RecA filament)
*RecA
LexA
active
represso
r
Lex
A
inactive
represso
r
Current value is 43 LexA-repressed genes
Variations in the sequence of LexA-binding sites means that LexA binds with
different affinities. Weak binding sites allow more frequent
dissociation/reassociation, but when dissociated RecA can stimulate selfcleavage
There is thus a hierarchy in derepression of SOS genes
Figure 11.19