, Volume 154, Issue 3, pp 225-230

Replication of plasmid pSC101 inEscherichia coli K12: Requirement fordnaA function

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Replication of pSC101 was analyzed by using DNA-DNA hybridization and alkaline sucrose gradient centrifugation. Mutants of thednaA gene were tested for their capacity to replicate pSC101 DNA at a non-permissive temperature. Only a small amount of radioactive precursor was incorporated into pSC101 DNA indnaA mutants at 42°C whereas active incorporation into plasmid DNA took place indnaA + strains under the same conditions. The effect of thednaA mutation was grater on plasmid DNA synthesis than on host chromosomal DNA synthesis. The numbers of copies of pSC101 per chromosome in wild type anddnaA strains, grown at 30°C, were about 8 and 2, respectively. These results indicate that thednaA gene product is required for the replication of pSC101 DNA.