THE PHAGE-LAMBDA ORF GENE ENCODES A TRANS-ACTING FACTOR THAT SUPPRESSES ESCHERICHIA-COLI RECO, RECR, AND RECF MUTATIONS FOR RECOMBINATION OF LAMBDA BUT NOT OF ESCHERICHIA-COLI

Bacteriophage lambda can recombine in recBC sbcB sbcC mutant cells by using its own gene orf, the Escherichia coli recO, recR, and recF gene s, or both. Expression of an orf-containing plasmid complements the re combination defects of orf mutant phage. However, this clone does not complement a recO mutation for conjugational recombination or recO, re cR, or recF mutations for repair of UV-induced DNA damage. A plasmid c lone of orf produces a protein with an apparent molecular mass of 15 k Da.