Coupling of transcription and DNA repair in bacteria is mediated by 
transcription-repair coupling factor (TRCF, the product of the mfd gene), which 
removes transcription elongation complexes stalled at DNA lesions and recruits 
the nucleotide excision repair machinery to the site. Here we describe the 3.2 
A-resolution X-ray crystal structure of Escherichia coli TRCF. The structure 
consists of a compact arrangement of eight domains, including a translocation 
module similar to the SF2 ATPase RecG, and a region of structural similarity to 
UvrB. Biochemical and genetic experiments establish that another domain with 
structural similarity to the Tudor-like domain of the transcription elongation 
factor NusG plays a critical role in TRCF/RNA polymerase interactions. 
Comparison with the translocation module of RecG as well as other structural 
features indicate that TRCF function involves large-scale conformational 
changes. These data, along with a structural model for the interaction of TRCF 
with the transcription elongation complex, provide mechanistic insights into 
TRCF function.