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The Bacteriophage P1 hot Gene Product Can Substitute for the Escherichia coli DNA Polymerase III Subunit

Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709,¹ D. I. Ivanovsky Institute of Virology, Russian Academy of Medical Science, Moscow, 123098, Russia²

Received 29 March 2005/ Accepted 20 May 2005

The subunit (holE gene product) of Escherichia coli DNA polymerase (Pol) III holoenzyme is a tightly bound component of the polymerase core. Within the core (--), the and subunits carry the DNA polymerase and 3' proofreading functions, respectively, while the precise function of is unclear. holE homologs are present in genomes of other enterobacteriae, suggestive of a conserved function. Putative homologs have also been found in the genomes of bacteriophage P1 and of certain conjugative plasmids. The presence of these homologs is of interest, because these genomes are fully dependent on the host replication machinery and contribute few, if any, replication factors themselves. To study the role of these homologs, we have constructed an E. coli strain in which holE is replaced by the P1 homolog, hot. We show that hot is capable of substituting for holE when it is assayed for its antimutagenic action on the proofreading-impaired dnaQ49 mutator, which carries a temperature-sensitive subunit. The ability of hot to substitute for holE was also observed with other, although not all, dnaQ mutator alleles tested. The data suggest that the P1 hot gene product can substitute for the subunit and is likely incorporated in the Pol III complex. We also show that overexpression of either or Hot further suppresses the dnaQ49 mutator phenotype. This suggests that the complexing of dnaQ49- with is rate limiting for its ability to proofread DNA replication errors. The possible role of hot for bacteriophage P1 is discussed.

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