title: Recombination hotspots and single-stranded DNA binding proteins couple DNA translocation to DNA unwinding by the AddAB helicase-nuclease.
abstract: AddAB is a helicase-nuclease that processes double-stranded DNA breaks for repair by homologous recombination. This process is modulated by Chi recombination hotspots: specific DNA sequences that attenuate the nuclease activity of the translocating AddAB complex to promote downstream recombination. Using a combination of kinetic and imaging techniques, we show that AddAB translocation is not coupled to DNA unwinding in the absence of single-stranded DNA binding proteins because nascent single-stranded DNA immediately re-anneals behind the moving enzyme. However, recognition of recombination hotspot sequences during translocation activates unwinding by coupling these activities, thereby ensuring the downstream formation of single-stranded DNA that is required for RecA-mediated recombinational repair. In addition to their implications for the mechanism of double-stranded DNA break repair, these observations may affect our implementation and interpretation of helicase assays and our understanding of helicase mechanisms in general.
authors.affiliation: DNA:Protein Interactions Unit, School of Biochemistry, Medical Sciences Building, University of Bristol, University Walk, Bristol BS8 1TD, UK.
authors.forename: Joseph T P
authors.initials: JT
authors.lastname: Yeeles
authors.forename: Kara
authors.initials: K
authors.lastname: van Aelst
authors.forename: Mark S
authors.initials: MS
authors.lastname: Dillingham
authors.forename: Fernando
authors.initials: F
authors.lastname: Moreno-Herrero
mesh_terms: D001412:Bacillus subtilis / Q000737:chemistry / Q000201:enzymology / Q000378:metabolism*; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism; D020029:Base Pairing; D004269:DNA, Bacterial / Q000737:chemistry / Q000378:metabolism*; D004277:DNA, Single-Stranded / Q000737:chemistry / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D005090:Exodeoxyribonucleases / Q000737:chemistry / Q000378:metabolism*; D011995:Recombination, Genetic
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D004277:DNA, Single-Stranded; D004268:DNA-Binding Proteins; D005090:Exodeoxyribonucleases; C407424:AddAB enzyme