title: DNA polymerase beta and flap endonuclease 1 enzymatic specificities sustain DNA synthesis for long patch base excision repair.
abstract: DNA polymerase beta (pol beta) and flap endonuclease 1 (FEN1) are key players in pol beta-mediated long-patch base excision repair (LP-BER). It was proposed that this type of LP-BER is accomplished through FEN1 removal of a 2- to 11-nucleotide flap created by pol beta strand displacement DNA synthesis. To understand how these enzymes might cooperate during LP-BER, we characterized purified human pol beta DNA synthesis by utilizing various BER intermediates, including single-nucleotide-gapped DNA, nicked DNA, and nicked DNA with various lengths of flaps all with a 5'-terminal tetrahydrofuran (THF) residue. We observed that nicked DNA and nicked-THF flap DNA were poor substrates for pol beta-mediated DNA synthesis; yet, DNA synthesis was strongly stimulated by purified human FEN1. FEN1 did not improve pol beta substrate binding. FEN1 cleavage activity was required for the stimulation, suggesting that FEN1 removed a barrier to pol beta DNA synthesis. In addition, FEN1 cleavage on both nicked and nicked-THF flap DNA resulted in a one-nucleotide gapped DNA molecule that was an ideal substrate for pol beta. This study demonstrates that pol beta cooperates with FEN1 to remove DNA damage via a "Hit and Run" mechanism, involving alternating short gap production by FEN1 and gap filling by pol beta, rather than through coordinated formation and removal of a strand-displaced flap.
authors.affiliation: Laboratory of Structural Biology, NIEHS, National Institutes of Health, Research Triangle Park, North Carolina 27709, USA.
authors.forename: Yuan
authors.initials: Y
authors.lastname: Liu
authors.forename: William A
authors.initials: WA
authors.lastname: Beard
authors.forename: David D
authors.initials: DD
authors.lastname: Shock
authors.forename: Rajendra
authors.initials: R
authors.lastname: Prasad
authors.forename: Esther W
authors.initials: EW
authors.lastname: Hou
authors.forename: Samuel H
authors.initials: SH
authors.lastname: Wilson
mesh_terms: D004247:DNA / Q000096:biosynthesis; D019951:DNA Polymerase beta / Q000235:genetics / Q000378:metabolism*; D004260:DNA Repair / Q000502:physiology*; D024202:Electrophoretic Mobility Shift Assay; D045585:Flap Endonucleases / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D013379:Substrate Specificity
chemical_list: D004247:DNA; D019951:DNA Polymerase beta; D045585:Flap Endonucleases