RNA polymerase signals UvrAB landing sites

Transcription when coupled to nucleotide excision repair specifies the location in active genes where preferential DNA repair is to take place. During DNA damage-induced recruitment of RNA polymerase (RNAP), there is a physical association of the beta subunit of Escherichia coli RNAP and the UvrA component of the repair apparatus (G. C. Lin and L. Grossman, submitted for publication). This molecular affinity is reflected in the ability of the RNAP to increase, in a promoter-dependent manner, DNA supercoiling by the UvrAB complex. In the presence of the RNAP, the UvrAB complex is able to bind to promoter regions and to translocate in a 5' to 3' direction along the non-transcribed strand. As a consequence of this helicase-catalyzed translocation, preferential incision of DNA damaged sites occurs downstream on the transcribed strand. Because of the helicase directionality, the initial binding of the UvrAB complex to the transcribed strand would inevitably lead to its collision with the RNAP. These results imply that the RNAP-induced DNA structure in the vicinity of the transcription start site signals a landing or entry site for the UvrAB complex on DNA.