Inducible expression of a gene specific to the RecF pathway for recombination in Escherichia coli K12.

The Mud(Aplac) operon fusion technique of Casadaban and Cohen (1979) was used to search for inducible functions specific to the RecF pathway of conjugal recombination. A fusion mutant of a recBC sbcB mutant which showed less than 1% of the normal level of recombination in Hfr crosses has been isolated and designated as rec-259. The mutation is shown to be closely linked to tyrA at approximately 57.5 min in relation to the standard genetic map, and is quite distinct from recA. Two point mutations within this gene have also been obtained. Mutation of this gene interferes specifically with the RecF pathway of recombination, and also causes increased sensitivity to mitomycin C and UV light. Expression of the lac genes in the rec-259 fusion strain is increased following damage to DNA, but not in lexA and recA derivatives. These observations demonstrate the existence of an inducible gene which is regulated by lexA and whose expression is required for RecF recombination and DNA repair.