title: DNA polymerase beta promotes recruitment of DNA ligase III alpha-XRCC1 to sites of base excision repair.
abstract: Base excision repair is a major pathway for the removal of simple lesions in DNA including base damage and base loss (abasic site). Base excision repair requires the coordinated action of several repair and ancillary proteins, the impairment of which can lead to genetic instability. Using a protein-DNA cross-linking assay during repair in human whole cell extracts, we monitored proteins involved in the initial steps of repair of a substrate containing a site-specific abasic site to address the molecular events following incision of the abasic site by AP endonuclease. We find that after dissociation of AP endonuclease from the incised abasic site, both DNA polymerase beta (Pol beta) and the DNA ligase IIIalpha-XRCC1 heterodimer efficiently bind/cross-link to the substrate DNA. We also find that the cross-linking efficacy of the DNA ligase IIIalpha-XRCC1 heterodimer was decreased about 2-fold in the Pol beta-deficient cell extract but was rescued by addition of purified wild type but not a mutant Pol beta protein that does not interact with the DNA ligase IIIalpha-XRCC1 heterodimer. We further demonstrate that Pol beta and the DNA ligase IIIalpha-XRCC1 heterodimer are present at equimolar concentrations in whole cell extracts and that Pol beta has a 7-fold higher affinity to the incised abasic site containing substrate than DNA ligase IIIalpha. Using gel filtration of whole cell extracts prepared at physiological salt conditions (0.15 M NaCl), we find no evidence for a stable preexisting complex of DNA Pol beta with the DNA ligase IIIalpha-XRCC1 heterodimer. Taken together, these data suggest that following incision by AP endonuclease, DNA Pol beta recognizes and binds to the incised abasic site and promotes recruitment of the DNA ligase IIIalpha-XRCC1 heterodimer through its interaction with XRCC1.
authors.affiliation: Radiation and Genome Stability Unit, Medical Research Council, Harwell, Oxfordshire OX11 0RD, UK.
authors.forename: Jason L
authors.initials: JL
authors.lastname: Parsons
authors.forename: Irina I
authors.initials: II
authors.lastname: Dianova
authors.forename: Sarah L
authors.initials: SL
authors.lastname: Allinson
authors.forename: Grigory L
authors.initials: GL
authors.lastname: Dianov
mesh_terms: D000818:Animals; D002457:Cell Extracts / Q000737:chemistry; D002460:Cell Line; D002850:Chromatography, Gel; D003432:Cross-Linking Reagents / Q000378:metabolism; D004249:DNA Damage; D000072481:DNA Ligase ATP; D011088:DNA Ligases / Q000378:metabolism*; D019951:DNA Polymerase beta / Q000737:chemistry* / Q000172:deficiency / Q000235:genetics; D004260:DNA Repair; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D019281:Dimerization; D006367:HeLa Cells; D006801:Humans; D051379:Mice; D018345:Mice, Knockout; D000075223:Poly-ADP-Ribose Binding Proteins; D011485:Protein Binding; D021381:Protein Transport; D000076105:X-ray Repair Cross Complementing Protein 1; D029867:Xenopus Proteins
chemical_list: D002457:Cell Extracts; D003432:Cross-Linking Reagents; D004268:DNA-Binding Proteins; D000075223:Poly-ADP-Ribose Binding Proteins; D000076105:X-ray Repair Cross Complementing Protein 1; C000619371:XRCC1 protein, human; D029867:Xenopus Proteins; C000619352:Xrcc1 protein, mouse; D019951:DNA Polymerase beta; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase; D011088:DNA Ligases; D000072481:DNA Ligase ATP; C000618816:DNA ligase III alpha protein, Xenopus; C000618817:LIG3 protein, human; C000618818:Lig3 protein, mouse