COOPERATION OF THE PRS AND DNAA GENE-PRODUCTS FOR INITIATION OF CHROMOSOME-REPLICATION IN ESCHERICHIA-COLI

A new Escherichia coli mutant allele, named dnaR, that causes thermose nsitive initiation of chromosome replication has been identified to be an allele of the prs gene, the gene for phosphoribosylpyrophosphate s ynthetase (Y. Sakakibara, J. Mol. Biol. 226:979-987, 1992; Y. Sakakiba ra, J. Mol. Biol. 226:989-9%, 1992). The dnaR mutant became temperatur e resistant by acquisition of a mutation in the dnaA gene that did not affect the intrinsic activity for the initiation of replication. The suppressor mutant was capable of initiating replication from oriC at a high temperature restrictive for the dnaR single mutant. The thermore sistant DNA synthesis was inhibited by the presence of the wild-type d naA allele at a high but not a low copy number. The synthesis was also inhibited by an elevated dose of a mutant dnaR allele retaining dnaR activity. Therefore, thermoresistant DNA synthesis in the suppressor m utant was dependent on both the dnaA and the dnaR functions. On the ba sis of these results, I conclude that the initiation of chromosome rep lication requires cooperation of the prs and dnaA products.