ATP-dependent renaturation of DNA catalyzed by the recA protein of Escherichia coli (ATPase/single-stranded DNA/lexB30 and tif-l mutants/cold-sensitive mutation/recombination intermediate)

The product of the recA gene of Escherichia coli has been purified to near-homogeneity by a simple three- step procedure. Incubation of the recA protein with comple- mentary single strands of DNA, Mg2e+ and ATP results in the rapid formation of large DNA aggregates containing many branched structures. As judged by resistance to SI nuclease and by electron microscopy, these aggregates contain both duplex and single-stranded regions. The renaturation and aggregation of DNA catalyzed by the recA protein is coupled to the hydrol- ysis of ATP. The recA protein purified from a cold-sensitive recA mutant does not catalyze DNA renaturation or aggregation at 28?C, but does so at 37?C, a finding which correlates with the recombination defect observed in vivo and indicates that this activity is an intrinsic function of the recA protein. These results suggest that the recA protein plays a specific role in strand transfer during recombination and possibly in postreplication repair of damaged DNA.