Isolation and genetic characterization of new uvsW alleles of bacteriophage T4.

The uvsW gene of bacteriophage T4 is required for wild-type levels of recombination, for normal survival and mutagenesis after UV irradiation, and for wild-type resistance to hydroxyurea. Additionally, uvsW mutations restore the arrested DNA synthesis caused by mutations in any of several genes that block secondary initiation (recombination-primed replication, the major mode of initiation at late times), but only partially restore the reduced burst size. A uvsW deletion mutation was constructed to establish the null-allele phenotype, which is similar but not identical to the phenotype of the canonical uvsW mutation, and to demonstrate convincingly that the uvsW gene is nonessential (although uvsW mutations severely compromise phage production). In an attempt to uncouple the diverse effects of uvsW mutations, temperature-sensitive uvsWts mutants were isolated. Recombination and replication effects were partially uncoupled in these mutants, suggesting distinct and separable roles for uvsW in the two processes. Furthermore, the restoration of DNA synthesis but not recombination in the double mutants uvsW uvsX and uvsW uvsY prompts the hypothesis that the restored DNA synthesis is not recombinationally initiated.