Mechanism of conjugation and recombination in bacteria XVI: single-stranded regions in recipient deoxyribonucleic acid during conjugation in Escherichia coli K-12.

The formation of mating pairs between F- and Hfr cells resulted in increased sensitivity of recipient deoxyribonucleic acid (DNA) to single-strand-specific S1 nuclease, from 3.6% to 23.5% after 30 min conjugation. A comparable amount of single strand regions in the DNA of mated wild type and recA mutant cells was detected. 10 min of conjugation resulted in almost the same amount of single-strand recipient DNA as 30 min of continuous transfer of donor DNA. Also the transfer of plasmid DNA from F+ recA strain led to the occurrence of single-strand recipient DNA. In similar experiments with Hfr tra mutant no such effect was observed. We conclude that alterations in the sechases of conjugation associated with the formation of mating pairs and/or initiation of transfer donor DNA.