Plasmid pSC101 replication in integratively suppressed cells requires dnaA function.

Maintenance of plasmid pKC17, a derivative of plasmid pSC101, in E. coli requires a functional dnaA gene product. This was demonstrated by segregation experiments using an E. coli dnaA46 mutant, at various temperatures. Growth of this mutant at elevated temperature was allowed by the presence of a P2sig5 prophage. rpoB mutations, which suppress the temperature sensitivity of a dnaA46 mutant permit efficient maintenance of plasmid pKC17 at temperatures up to 40 degrees, conditions which normally inactivate the dnaA46 product.