Heterodimer formation between Escherichia coli rep and UvrD proteins

DNA helicases catalyze the essential process of unwinding duplex DNA to form the single-stranded DNA intermediates required for DNA metabolic processes including replication, recombination, and repair. Most cells, possibly all, encode multiple helicases that function selectively in different processes, although some helicases can complement each other in vivo. Thus, although Escherichia coli can survive mutations or deletions of either the uvrD gene (encoding Helicase II) or the rep gene (encoding Rep helicase) separately, deletion of both rep and uvrD genes is lethal (Washburn, B. K., and Kushner, S. R. (1991) J. Bacteriol. 173, 2569-2575). The Rep and UvrD polypeptides share ∼40% sequence homology, and we have previously shown that both form homodimeric species and that the Rep homodimer appears to be the functionally active helicase. We report here that these two proteins can also interact in vitro to form a heterodimer. The heterodimer appears to be energetically more stable than the Rep homodimer but less stable than the UvrD homodimer under our conditions. The observation of Rep/UvrD heterodimer formation in vitro opens up the intriguing possibility that the heterodimer may play a physiologically important role that is distinct from the role of the Rep or UvrD homodimers. Therefore, considerations of the role of either protein in DNA metabolic processes, such as replication and repair, must include a potential role for a Rep/UvrD heterodimer.