Transcription and DNA repair are coupled in E. coli by the Mfd protein, which 
dissociates transcription elongation complexes blocked at nonpairing lesions and 
mediates recruitment of DNA repair proteins. We show that Mfd influences the 
elongation state of RNA polymerase (RNAP); transcription complexes that have 
reverse translocated into the backtracked position, a potentially important 
intermediate in RNA proofreading and repair, are restored to the forward 
position by the activity of Mfd, and arrested complexes are rescued into 
productive elongation. Mfd may act through a translocase activity that rewinds 
upstream DNA, leading either to translocation or to release of RNA polymerase 
when the enzyme active site cannot continue elongation.