Mutants of Escherichia coli B/r Defective in Deoxyribonucleic Acid Initiation: dnaI , a New Gene for Replication

Abstract

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.