Transcription-Coupled DNA Repair in Prokaryotes - Progress in Molecular Biology - page 34

UvrA binding DNA binding and bending UvrA /UvrC binding

I Ia II III IV V VI

100 200 300 400 500 600

D1a D2 D1b D3 D4

F IG . 4. Schematic linear representation of the UvrB protein (adapted from Refs. 55,56 ). The
UvrA-binding region in the amino-terminal domain is homologous to the UvrA-binding region of
Mfd . The carboxyl-terminal domain, D4 (gray), is an autoinhibitory domain. 57 The UvrA-binding
region in D4 overlaps the UvrC-binding site. The helicase motifs, shown in red in D1a and D3,
participate in DNA binding. Numbers below the bars refer to amino acids.

UvrA to the DNA at the site of the arrested polymerase, after Mfd dissociated,
UvrB should recognize the damage on the nontranscribed strand, bind to it,
and attract UvrC. To our knowledge, this situation has not been observed.

VII. Other Examples of Transcription-Related DNA Damage
Processing in Bacteria

Several reports have described phenomena associated with transcription
and termed TCR; however, in some cases, the studies do not include direct
measurements of DNA damage removal or results showing that the transcribed
strand of an active gene is repaired more rapidly than the nontranscribed
strand. We have used the term ''transcription-related DNA damage processing''
for these responses until more information becomes available.

A. NusA
The relatively neat picture of TCR involving RNA polymerase, Mfd , and the
UvrAB* complex has become more complicated with the observation that the
transcription terminator/antiterminator NusA may also be implicated. In fact,
NusA may be involved in two forms of transcription-related DNA damage
processing, one being Mfd dependent and the other being Mfd independent.
Support for this idea comes from studies of the effect of nusA mutants on the
survival of several derivatives of E. coli K-12 treated with nitrofurazone, NQO,
MMS, or UV, together with the evidence that NusA associates with the '

subunits of the bacterial RNA polymerase and with UvrA 58-61 ;however,nodirect
evaluation of its effect on DNA damage removal has been reported. To evaluate
the role of NusA, in repair it will be essential to measure lesion removal in nusA

b and b