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Structure/Function Analysis of the Interaction of Adenomatous Polyposis Coli with DNA Polymerase β and Its Implications for Base Excision Repair

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posted on 11.12.2007, 00:00 by Ramesh Balusu, Aruna S. Jaiswal, Melissa L. Armas, Chanakya N. Kundu, Linda B. Bloom, Satya Narayan
Mutations in the adenomatous polyposis coli (APC) gene are associated with an early onset of colorectal carcinogenesis. Previously, we described a novel role for the APC polypeptide in base excision repair (BER). The single-nucleotide (SN) and long-patch (LP) BER pathways act to repair the abasic sites in DNA that are induced by stressors, such as spontaneous oxidation/reduction, alkylation, and hyperthermia. We have shown that APC interacts with DNA polymerase β (Pol-β) and flap endonuclease 1 (Fen-1) and blocks Pol-β-directed strand-displacement synthesis. In this study, we have mapped the APC interaction site in Pol-β and have found that Thr79, Lys81, and Arg83 of Pol-β were critical for its interaction with APC. The Pol-β protein (T79A/K81A/R83A) blocked strand-displacement DNA synthesis in which tetrahydrofuran was used as DNA substrate. We further showed that the APC-mediated blockage of LP-BER was due to inhibition of Fen-1 activity. Analysis of the APC-mediated blockage of SN-BER indicated that the interaction of APC with Pol-β blocked SN-BER activity by inhibiting Pol-β-directed deoxyribose phosphate lyase activity. Collectively, our findings indicate that APC blocked both Pol-β-directed SN- and LP-BER pathways and increased sensitivity of cells to alkylation induced DNA damage.

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