Conjugational synthesis of F lac+ and Col I DNA in the presence of rifampicin and in Escherichia coli K12 mutants defective in DNA synthesis.

Abstract

When F lac+ donors were mixed with irradiated recipient bacteria, there was a stimulation of DNA synthesis in the recipients equivalent to the amount of DNA transferred. Rifampicin had little effect on such conjugational synthesis of F′ and ColI DNA during the first 30 min of mating. In matings of temperature-sensitive (ts) dnaB70 mutants at 43° C, transfer of F lac+ and ColI DNA was associated with an equal amount of conjugational DNA synthesis in the two parents, the amounts being unaffected by the polA1 mutation. Rifampicin abolished conjugational DNA synthesis in dnaB recipients mated with rifampicinresistant F lac+ donors but it stimulated synthesis in equivalent matings involving ColI. Although F lac+ and ColI DNA was transferred to (ts) dnaE486 mutants at 43° C, transfer was not associated with either enhanced DNA synthesis in the recipients or the extensive synthesis in them of DNA which was convertible into covalently closed circular molecules by brief incubation at a permissive temperature. These results imply that DNA polymerase III is essential for synthesis of the strands complementary to the transferred F- and I-like plasmid DNA. In the case of ColI, the process is resistant to rifampicin both in the presence and absence of dnaB function whereas for F lac+, it is sensitive when dnaB gene product is thermally inactivated.