DNA polymerase Beta promotes recruitment of XRCC1-Ligase III alpha to sites of base excision repair.

Parsons, Jason L. and Dianova, Irina I. and Allinson, Sarah L. and Dianov, Grigory L. (2005) DNA polymerase Beta promotes recruitment of XRCC1-Ligase III alpha to sites of base excision repair. Biochemistry, 44 (31). pp. 10613-10619. ISSN 0006-2960

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 (Pol ) and the DNA ligase III-XRCC1 heterodimer efficiently bind/cross-link to the substrate DNA. We also find that the cross-linking efficacy of the DNA ligase III-XRCC1 heterodimer was decreased about 2-fold in the Pol -deficient cell extract but was rescued by addition of purified wild type but not a mutant Pol protein that does not interact with the DNA ligase III-XRCC1 heterodimer. We further demonstrate that Pol and the DNA ligase III-XRCC1 heterodimer are present at equimolar concentrations in whole cell extracts and that Pol has a 7-fold higher affinity to the incised abasic site containing substrate than DNA ligase III. 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 with the DNA ligase III-XRCC1 heterodimer. Taken together, these data suggest that following incision by AP endonuclease, DNA Pol recognizes and binds to the incised abasic site and promotes recruitment of the DNA ligase III-XRCC1 heterodimer through its interaction with XRCC1.