Uvr-independent repair of 8-methoxypsoralen crosslinks in Escherichia coli: evidence for a recombinational process.

On the basis of survival data, repair of 8-methoxypsoralen DNA crosslinks in Escherichia coli strains lacking a functional uvrABC endonuclease, is shown to require the products of the recA, recB, recF and recN genes. Bacteria, grown under conditions where most cells contain only a single genome, show no evidence of crosslink repair. Similarly, bacteriophage lambda shows evidence of crosslink repair only in SOS-induced cells, and only at multiplicities of infection greater than 1. The requirement for rec+ genes may be partly ascribed to the need for a functional SOS response, but taken together, the results suggest a recombinational step involving a homologous region of DNA may occur during uvr-independent crosslink repair.