NOVEL Escherichia coli dnaB mutant: direct involvement of the dnaB252 gene product in the synthesis of an origin-ribonucleic acid species during initiaion of a round of deoxyribonucleic acid replication

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Abstract
The initiation process of DNA replication in E. coli was studied using the thermoreversible dna initiation mutant E. coli HfrH165/120/6 dna-252. This dna mutation was incorrectly classed as a dnaA mutation. Biochemical and genetic evidence suggests that the dna-252 mutant is a novel dnaB mutant, possessing phenotypic properties which distinguish it from other dnaB mutants. Sensitivity of reinitiation in the dna-252 mutant to specific inhibitors of protein, RNA and DNA synthesis was studied. Reinitiation is sensitive to rifampin and streptolydigin but not to chloramphenicol. Thus, the dna-252 gene product appears to be required during the initiation process for a step occurring before or during synthesis of an RNA species (origin-RNA). Reversible inhibition of RNA synthesis by streptolydigin of a streptolydigin-sensitive derivative of the dna-252 mutant showed that the dna-252 gene product is directly involved in the synthesis of an origin-RNA species. These results are included in a schematic model of the temporal sequence of events occurring during the initiation process.