title: DNA branch nuclease activity of vaccinia A22 resolvase.
abstract: DNA replication, recombination, and repair can result in formation of diverse branched DNA structures. Many large DNA viruses are known to encode DNA branch nucleases, but several of the expected activities have not previously been found among poxvirus enzymes. Vaccinia encodes an enzyme, A22 resolvase, which is known to be active on four-stranded DNA junctions (Holliday junctions) or Holliday junction-like structures containing three of the four strands. Here we report that A22 resolvase in fact has a much wider substrate specificity than previously appreciated. A22 resolvase cleaves Y-junctions, single-stranded DNA flaps, transitions from double strands to unpaired single strands ("splayed duplexes"), and DNA bulges in vitro. We also report site-directed mutagenesis studies of candidate active site residues. The results identify the likely active site and support a model in which a single active site is responsible for cleavage on Holliday junctions and splayed duplexes. Lastly, we describe possible roles for the A22 resolvase DNA-branch nuclease activity in DNA replication and repair.
authors: Department of Microbiology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104-6076, USA.
authors: Matthew J
authors: MJ
authors: Culyba
authors: Nana
authors: N
authors: Minkah
authors: Young
authors: Y
authors: Hwang
authors: Ori-Michael J
authors: OM
authors: Benhamou
authors: Frederic D
authors: FD
authors: Bushman
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D004247:DNA / Q000737:chemistry*; D045566:DNA, Cruciform / Q000737:chemistry; D045565:Holliday Junction Resolvases / Q000737:chemistry; D008957:Models, Genetic; D008968:Molecular Conformation; D008969:Molecular Sequence Data; D016296:Mutagenesis; D016297:Mutagenesis, Site-Directed; D009690:Nucleic Acid Conformation; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity; D013696:Temperature; D014616:Vaccinia virus / Q000201:enzymology*
chemical_list: D045566:DNA, Cruciform; D004247:DNA; D045565:Holliday Junction Resolvases