Enhanced recombination between lambda plac5 and mini-F-lac: the tra regulon is required for recombination enhancement

F42lac recombination with lambda plac is normally 20-fold to 50-fold higher than recombination between lambda plac and a chromosomal lac gene. Transductional crosses with lambda plac and a recombinant plasmid containing the lac operon and F replication functions show only two to four-fold higher recombination than similar crosses with a chromosomal lac gene. Insertion of a BamHI fragment containing the entire tra regulon of F into the mini-F-lac plasmid restores the high level of recombination seen with F42lac.