RecA protein promotes the regression of stalled replication forks in vitro

Replication forks are halted by many types of DNA damage. At the site of a leading-strand DNA lesion, forks may stall and leave the lesion in a single -strand gap. Fork regression is the first step in several proposed pathways that permit repair without generating a double-strand break. Using model D NA substrates designed to mimic one of the known structures of a fork stall ed at a leading-strand lesion, we show here that RecA protein of Escherichi a coli will promote a fork regression reaction in vitro. The regression pro cess exhibits an absolute requirement for ATP hydrolysis and is enhanced wh en dATP replaces ATP. The reaction is not affected by the inclusion of the RecO and R proteins. We present this reaction as one of several potential R ecA protein roles in the repair of stalled and/or collapsed replication for ks in bacteria.