A new sub‐pathway of long‐patch base excision repair involving 5′ gap formation

Abstract

Base excision repair ( BER ) is one of the most frequently used cellular DNA repair mechanisms and modulates many human pathophysiological conditions related to DNA damage. Through live cell and in vitro reconstitution experiments, we have discovered a major sub‐pathway of conventional long‐patch BER that involves formation of a 9‐nucleotide gap 5′ to the lesion. This new sub‐pathway is mediated by RECQ 1 DNA helicase and ERCC 1‐ XPF endonuclease in cooperation with PARP 1 poly( ADP ‐ribose) polymerase and RPA . The novel gap formation step is employed during repair of a variety of DNA lesions, including oxidative and alkylation damage. Moreover, RECQ 1 regulates PARP 1 auto‐( ADP ‐ribosyl)ation and the choice between long‐patch and single‐nucleotide BER , thereby modulating cellular sensitivity to DNA damage. Based on these results, we propose a revised model of long‐patch BER and a new key regulation point for pathway choice in BER . image DNA base excision repair ( BER ) is essential for coping with highly frequent oxidative and alkylation base damage. Identification of a novel sub‐pathway argues for a revision of mammalian long‐patch BER models and suggests a new key regulation point in BER pathway choice. Live cell and in vitro reconstitution experiments reveal formation of a 9‐nucleotide gap 5′ to the lesion. Gap formation happens during repair of various DNA lesions, including oxidative and alkylation damage. Gap formation involves the specific actions of PARP1, RECQ1 helicase, RPA and ERCC1‐XPF endonuclease. RECQ1 inhibits PARP1 auto‐PARylation to suppress single‐nucleotide BER in favor of gap‐mediated long‐patch BER.