The bacteriophage P1 hot gene product is a homolog of the θ subunit of E. coli DNA polymerase III. Previous studies with hot cloned on a plasmid have shown that Hot protein can substitute for θ, as evidenced by its stabilizing effect on certain dnaQ mutator mutants carrying an unstable pol III proofreading subunit (ε subunit). These results are consistent with Hot, like θ, being a replication protein involved in stabilizing the intrinsically unstable ε proofreading function. However, the function of hot for the viral life cycle is less clear. In the present study, we show that the hot gene is not essential. Based on its promoter structure, hot has been previously classified as a "late" phage gene, a property that is not easily reconciled with a presumed replication function. Here, we clarify this issue by demonstrating that P1 hot is actively expressed both during the lysogenic state and in the early stages of a lytic induction, in addition to its expression in the late stage of phage development. The results indicate that P1 hot has a complex expression pattern, compatible with a model in which Hot may affect the host replication machinery to benefit overall phage replication.
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