title: Roles of DNA ligase III and XRCC1 in regulating the switch between short patch and long patch BER.
abstract: Damaged DNA bases are repaired by base excision repair (BER), which can proceed via two pathways: short patch and long patch BER. During the latter, a stretch of several nucleotides is replaced by strand displacement DNA synthesis. We recently demonstrated that the ATP concentration may govern the decision between these BER sub-pathways. Employing a reconstituted BER complex containing among others DNA polymerase beta (Pol beta), DNA ligase III (Lig III) and XRCC1, here we show that Lig III and XRCC1 are essential mediators of this regulation. XRCC1 stimulates Pol beta strand displacement activity and releases inhibition of Pol beta by DNA-bound Lig III if ligation is prevented. XRCC1 is thus able to strongly promote strand displacement and long patch BER under conditions of ATP shortage. If sufficient ATP is available, ligation by Lig III prevents strand displacement, leading to short patch BER. Ligation-inactive mutants of Lig III do not prevent strand displacement by Pol beta under the same conditions. Consequently, the preferred use of short patch BER depends on the ligation competence of Lig III. Accordingly, lowering the levels of the XRCC1/Lig III complex in HeLa cells using siRNA decreases ligation capacity but enhances Pol beta-dependent DNA synthesis.
authors.affiliation: Institut für Biochemie, Freie Universität Berlin, Thielallee 63, 14195 Berlin, Federal Republic of Germany.
authors.forename: Eva
authors.initials: E
authors.lastname: Petermann
authors.forename: Claudia
authors.initials: C
authors.lastname: Keil
authors.forename: Shiao Li
authors.initials: SL
authors.lastname: Oei
mesh_terms: D021581:Active Transport, Cell Nucleus; D000255:Adenosine Triphosphate / Q000378:metabolism; D001483:Base Sequence; D000072481:DNA Ligase ATP; D011088:DNA Ligases / Q000235:genetics / Q000378:metabolism*; D019951:DNA Polymerase beta / Q000378:metabolism; D004260:DNA Repair / Q000502:physiology*; D018076:DNA, Complementary / Q000235:genetics; D004268:DNA-Binding Proteins / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D066298:In Vitro Techniques; D008954:Models, Biological; D016297:Mutagenesis, Site-Directed; D000075223:Poly-ADP-Ribose Binding Proteins; D034741:RNA, Small Interfering / Q000235:genetics; D000076105:X-ray Repair Cross Complementing Protein 1; D029867:Xenopus Proteins
chemical_list: D018076:DNA, Complementary; D004268:DNA-Binding Proteins; D000075223:Poly-ADP-Ribose Binding Proteins; D034741:RNA, Small Interfering; D000076105:X-ray Repair Cross Complementing Protein 1; C000619371:XRCC1 protein, human; D029867:Xenopus Proteins; D000255:Adenosine Triphosphate; D019951:DNA Polymerase beta; D011088:DNA Ligases; D000072481:DNA Ligase ATP; C000618816:DNA ligase III alpha protein, Xenopus; C000618817:LIG3 protein, human