title: The phage T4 protein UvsW drives Holliday junction branch migration.
abstract: The phage T4 UvsW protein has been shown to play a crucial role in the switch from origin-dependent to recombination-dependent replication in T4 infections through the unwinding of origin R-loop initiation intermediates. UvsW also functions with UvsX and UvsY to repair damaged DNA through homologous recombination, and, based on genetic evidence, has been proposed to act as a Holliday junction branch migration enzyme. Here we report the purification and characterization of UvsW. Using oligonucleotide-based substrates, we confirm that UvsW unwinds branched DNA substrates, including X and Y structures, but shows little activity in unwinding linear duplex substrates with blunt or single-strand ends. Using a novel Holliday junction-containing substrate, we also demonstrate that UvsW promotes the branch migration of Holliday junctions efficiently through more than 1000 bp of DNA. The ATP hydrolysis-deficient mutant protein, UvsW-K141R, is unable to promote Holliday junction branch migration. However, both UvsW and UvsW-K141R are capable of stabilizing Holliday junctions against spontaneous branch migration when ATP is not present. Using two-dimensional agarose gel electrophoresis we also show that UvsW acts on T4-generated replication intermediates, including Holliday junction-containing X-shaped intermediates and replication fork-shaped intermediates. Taken together, these results strongly support a role for UvsW in the branch migration of Holliday junctions that form during T4 recombination, replication, and repair.
authors.affiliation: Department of Biochemistry, Duke University Medical Center, Durham, NC 27710, USA.
authors.forename: Michael R
authors.initials: MR
authors.lastname: Webb
authors.forename: Jody L
authors.initials: JL
authors.lastname: Plank
authors.forename: David T
authors.initials: DT
authors.lastname: Long
authors.forename: Tao-shih
authors.initials: TS
authors.lastname: Hsieh
authors.forename: Kenneth N
authors.initials: KN
authors.lastname: Kreuzer
mesh_terms: D019943:Amino Acid Substitution; D017122:Bacteriophage T4 / Q000502:physiology*; D004249:DNA Damage / Q000502:physiology*; D004265:DNA Helicases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004260:DNA Repair / Q000502:physiology*; D004261:DNA Replication / Q000502:physiology*; D045566:DNA, Cruciform / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004277:DNA, Single-Stranded / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D020125:Mutation, Missense; D011995:Recombination, Genetic / Q000502:physiology; D014764:Viral Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D014779:Virus Replication / Q000502:physiology*