Practice question

Single-stranded DNA preference of RecA ensures that recombinogenic ends not double-stranded regions are targeted. ssDNA generated after resection or RecBCD processing is immediately bound by SSB in bacteria or RPA in eukaryotes, which melts secondary structures. RecA mediator proteins such as RecFOR facilitate replacement of SSB with cooperative ATP-bound RecA nucleating into contiguous filament. Within filament ssDNA adopts extended conformation facilitating base-triplet scanning for homology on intact duplex. This selective binding avoids illegitimate association with undamaged chromosomes, channeling strand invasion specifically to broken resected termini requiring repair.