The bacteriophage lambda replication initiation protein P exhibits a toxic effect on its
Escherichia coli (
E. coli) host, likely due to the formation of a dead-end P-DnaB complex, sequestering the replicative DnaB helicase from further activity. Intracellular expression of P triggers
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The bacteriophage lambda replication initiation protein P exhibits a toxic effect on its
Escherichia coli (
E. coli) host, likely due to the formation of a dead-end P-DnaB complex, sequestering the replicative DnaB helicase from further activity. Intracellular expression of P triggers SOS-independent cellular filamentation and rapidly cures resident ColE1 plasmids. The toxicity of P is suppressed by alleles of
P or
dnaB. We asked whether P buildup within a cell can influence
E. coli replication fidelity. The influence of P expression from a defective prophage, or when cloned and expressed from a plasmid was examined by screening for auxotrophic mutants, or by selection for rifampicin resistant (Rif
R) cells acquiring mutations within the
rpoB gene encoding the β-subunit of RNA polymerase (RNAP), nine of which proved unique. Using fluctuation assays, we show that the intracellular expression of P evokes a mutator effect. Most of the Rif
R mutants remained P
S and localized to the Rif binding pocket in RNAP, but a subset acquired a P
R phenotype, lost sensitivity to ColE1 plasmid curing, and localized outside of the pocket. One P
R mutation was identical to rpo*Q148P, which alleviates the UV-sensitivity of
ruv strains defective in the migration and resolution of Holliday junctions and destabilizes stalled RNAP elongation complexes. The results suggest that P-DnaB sequestration is mutagenic and supports an earlier observation that P can interact with RNAP.
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