Mutants of Escherichia coli B-r defective in deoxyribonucleic acid initiation: dnaI, a new gene for replication.

Mutagenized E. coli B/r cells were subjected to a procedure designed to select mutants temperature-sensitive for initiation of deoxyribonucleic acid (DNA) replication. Seventeen mutants exhibiting limited residual DNA synthesis at 42 C were obtained and the dna(-) sites were mapped genetically. Sixteen of the sites map near dnaA, dnaB, and dnaC. One mutant (dna-208) maps in a new location between the trp and his genes. We propose to call this mutant dnaI208. In complementation experiments dnaC(+) and dnaI(+) were dominant to dnaC(-) and dnaI(-) alleles, respectively. However, dnaA(-) was dominant to the wild-type allele dnaA(+). All dnaA mutants and four out of six dnaC mutants could be suppressed by F factor integration. The pattern of suppression was specific for each mutant.