The bacterial Mfd protein is a transcription-repair coupling factor that 
performs two key functions during transcription-coupled DNA repair. The first is 
to remove RNA polymerase (RNAP) complexes that have been stalled by a DNA lesion 
from the site of damage, and the second is to mediate the recruitment of DNA 
repair proteins. Mfd also displaces transcription complexes that have been 
stalled by protein roadblocks, and catalyses the reactivation of transcription 
complexes that have become 'backtracked'. We have identified amino acid 
substitutions in the beta subunit of Escherichia coli RNAP that disrupt a direct 
interaction between Mfd and RNAP. These substitutions prevent Mfd displacing 
stalled RNAP from DNA in vivo and in vitro. They define a highly conserved 
surface-exposed patch on the beta1 domain of RNAP that is required by Mfd for 
the initial step of transcription-coupled repair, the enhancement of roadblock 
repression and the reactivation of backtracked transcription complexes.