Specialized transduction with lambda plac5: involvement of the RecE and RecF recombination pathways

Several aspects of the recombination resulting from lambda plac5 transduction were investigated in strains of Escherichia coli K-12 that use the RecE or RecF recombination pathways. In a RecBC pathway strain, F42lac recombination with lambda plac5 is 20- to 50-fold higher than chromosomal lac times lambda plac5 recombination, and this recombination enhancement is largely dependent on constitutive expression of F42lac fertility functions. Here, it was observed that F42lac fertility functions do not effect the ability of F42lac to recombine with lambda plac5 in a RecE or RecF pathway strain. Therefore, the enhancement observed in a Rec+ (or RecBC pathway) strain is directly dependent on the recBC gene product. The end product of recombination between lambda plac5 and either F42lac or chromosomal lac in RecE and RecF pathway strains was monitored by scoring for addition and substitution transductants. It was observed that the percentage of addition transductants was lower in all cases for RecE and RecF pathway strains as compared with RecBC pathway or a recB strain. It is concluded that the introduction of sbcA or sbcB into a recB strain produces a change in recombination mechanism that is reflected in the nature of the end product of recombination.