Mechanism of conjugation and recombination in bacteria. XVII. Further evidence for single-stranded regions in recipient DNA during conjugation in Escherichia coli K-12.

The secondary structure of recipient DNA mated with Hfr strain was investigated by CsCl density gradient fractionation. After 45 min of HfrH64 X 3h-f-ab1157 mating one-fourth of the radioactive recipient DNA was recovered as a single-strand but only after shearing of cell lysates prior to centrifugation. This heavier than native DNA fraction of radioactive material (obtained after the first centrifugation) was degraded by single-strand specific nuclease S from Aspergillus oryzae. These findings thus confirm the authors' earlier results suggesting that in the course of mating are generated local single-stranded regions in recipient DNA.