A protein produced by male strains of Escherichia coli K-12 which increases the yield of recombinants in conjugation: its nature and mode of action

Summary A protein present in filtrates of E. coli K-12 male strains is responsible for their ability to increase the yield of recombinants in conjugation and to inhibit nitrogen mustard after-effect (NMAE) in F ^- cells. The protein, designated recombination-stimulating factor (RSF), was purified 200–300 times from HfrC filtrate. Two Rsf^- mutants of strain HfrC were isolated which fail to produce RSF; these mutations affect an episomal gene. RSF action involves the attachment of RSF to the F ^- cell surface and requires the integrity of the RSF-cell complex. Some step of recombination after the transfer of the donor chromosomal fragment into the recipient is affected by RSF.