title: DNA helicase requirements for DNA replication during bacteriophage T4 infection.
abstract: The lytic bacteriophage T4 uses multiple mechanisms to initiate the replication of its DNA. Initiation occurs predominantly at replication origins at early times of infection, but there is a switch to genetic recombination-dependent initiation at late times of infection. The T4 insertion-substitution system was used to create a deletion in the T4 dda gene, which encodes a 5'-3' DNA helicase that stimulates both DNA replication and recombination reactions in vitro. The deletion caused a delay in T4 DNA synthesis at early times of infection, suggesting that the Dda protein is involved in the initiation of origin-dependent DNA synthesis. However, DNA synthesis eventually reached nearly wild-type levels, and the final number of phages produced per bacterium was similar to that of the wild type. When the dda mutant phage also contained a mutation in T4 gene 59 (a gene normally required only for recombination-dependent DNA replication), essentially no DNA was synthesized. Recent in vitro studies have shown that the gene 59 protein loads a component of the primosome, the T4 gene 41 DNA helicase, onto DNA. A molecular model for replication initiation is presented that is based on our genetic data.
authors.affiliation: Department of Science, Western State College, Gunnison, Colorado 81231.
authors.forename: P
authors.initials: P
authors.lastname: Gauss
authors.forename: K
authors.initials: K
authors.lastname: Park
authors.forename: T E
authors.initials: TE
authors.lastname: Spencer
authors.forename: K J
authors.initials: KJ
authors.lastname: Hacker
mesh_terms: D017122:Bacteriophage T4 / Q000201:enzymology* / Q000235:genetics; D001483:Base Sequence; D004265:DNA Helicases / Q000235:genetics / Q000502:physiology*; D004261:DNA Replication / Q000235:genetics / Q000502:physiology*; D004279:DNA, Viral / Q000096:biosynthesis*; D004926:Escherichia coli; D017353:Gene Deletion; D005814:Genes, Viral / Q000235:genetics / Q000502:physiology*; D008969:Molecular Sequence Data; D011995:Recombination, Genetic / Q000235:genetics / Q000502:physiology
chemical_list: D004279:DNA, Viral; D004265:DNA Helicases