The isolation and characterization of escherichia coli dnaB::Tn10 insertion mutations.

Exploitation of the ability of the ban protein encoded by phage P1 to compensate for dnaB-defective host mutations, allowed the isolation of dnaB::Tn10 insertion mutations. The presence of P1bac prophage was required for survival of dnaB::Tn10 mutants, and such lysogens were cryosensitive. The insertions were shown to map in dnaB by transduction and this was confirmed by complementation analysis. The dnaB::Tn10 (P1bac) strains were non-permissive for lambda growth but did support the growth of lambda-dnaB+ specialized transducing phage. No antigenically active dnaB product could be detected by immunologic assays using either of two methods. In addition, it was shown that the observe cryosensitivity of P1bac suppression was a direct result of reversible inactivation of the ban protein at low temperature.