Analysis of the R16 plasmid primase gene

The cloned genetic determinant of R16 (IncB) plasmid primase encodes two polypeptides (apparent Mr 240,000 and 175,000), probably products of the same coding sequence of DNA, which are also detectable in extracts of cells carrying the parent plasmid. Deletion analysis and transposon mutagenesis indicate that only about 1.7 kilobase pairs (kb) of the cloned fragment, encoding a truncated polypeptide of 76,000 Da, is necessary for activity. The cloned genetic determinant of the R387 (IncK) plasmid primase, which encodes polypeptides of apparent Mr 270,000 and 200,000, appears to be very similar to the R16 gene except for an additional sequence of approximately 0.65 kb.