title: Analysis of conserved basic residues associated with DNA binding (Arg69) and catalysis (Lys76) by the RusA holliday junction resolvase.
abstract: Holliday junctions are key intermediates in both homologous recombination and DNA repair, and are also formed from replication forks stalled at lesions in the template strands. Their resolution is critical for chromosome segregation and cell viability, and is mediated by a class of small, homodimeric endonucleases that bind the structure and cleave the DNA. All the enzymes studied require divalent metal ions for strand cleavage and their active centres are characterised by conserved aspartate/glutamate residues that provide ligands for metal binding. Sequence alignments reveal that they also contain a number of conserved basic residues. We used site-directed mutagenesis to investigate such residues in the RusA resolvase. RusA is a 120 amino acid residue polypeptide that can be activated in Escherichia coli to promote recombination and repair in the absence of the Ruv proteins. The RuvA, RuvB and RuvC proteins form a complex on Holliday junction DNA that drives coupled branch migration (RuvAB) and resolution (RuvC) reactions. In contrast to RuvC, the RusA resolvase does not interact directly with a branch migration motor, which simplifies analysis of its resolution activity. Catalysis depends on three highly conserved acidic residues (Asp70, Asp72 and Asp91) that define the catalytic centre. We show that Lys76, which is invariant in RusA sequences, is essential for catalysis, but not for DNA binding, and that an invariant asparagine residue (Asn73) is required for optimal activity. Analysis of DNA binding revealed that RusA may interact with one face of an open junction before manipulating its conformation in the presence of Mg(2+) as part of the catalytic process. A well-conserved arginine residue (Arg69) is linked with this critical stage. These findings provide the first insights into the roles played by basic residues in DNA binding and catalysis by a Holliday junction resolvase.
authors.affiliation: Institute of Genetics, University of Nottingham, Nottingham, NG7 2UH, UK.
authors.forename: E L
authors.initials: EL
authors.lastname: Bolt
authors.forename: G J
authors.initials: GJ
authors.lastname: Sharples
authors.forename: R G
authors.initials: RG
authors.lastname: Lloyd
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution / Q000235:genetics; D001120:Arginine / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D001665:Binding Sites; D002384:Catalysis; D017124:Conserved Sequence; D004247:DNA / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004249:DNA Damage / Q000528:radiation effects; D004265:DNA Helicases; D004260:DNA Repair / Q000235:genetics; D004268:DNA-Binding Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D004706:Endodeoxyribonucleases / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000166:cytology / Q000201:enzymology* / Q000235:genetics / Q000528:radiation effects; D029968:Escherichia coli Proteins; D045565:Holliday Junction Resolvases; D008239:Lysine / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D009690:Nucleic Acid Conformation; D011485:Protein Binding; D011995:Recombination, Genetic / Q000235:genetics; D016415:Sequence Alignment; D014466:Ultraviolet Rays
chemical_list: D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; C061260:RuvB protein, Bacteria; C069806:ruvC protein, E coli; D004247:DNA; D001120:Arginine; D004706:Endodeoxyribonucleases; D045565:Holliday Junction Resolvases; C112057:RusA protein, E coli; C071059:Holliday junction DNA helicase, E coli; D004265:DNA Helicases; D008239:Lysine