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  • Title: Human BRCA1-BARD1 ubiquitin ligase activity counteracts chromatin barriers to DNA resection.
    Author: Densham RM, Garvin AJ, Stone HR, Strachan J, Baldock RA, Daza-Martin M, Fletcher A, Blair-Reid S, Beesley J, Johal B, Pearl LH, Neely R, Keep NH, Watts FZ, Morris JR.
    Journal: Nat Struct Mol Biol; 2016 Jul; 23(7):647-55. PubMed ID: 27239795.
    Abstract:
    The opposing activities of 53BP1 and BRCA1 influence pathway choice in DNA double-strand-break repair. How BRCA1 counteracts the inhibitory effect of 53BP1 on DNA resection and homologous recombination is unknown. Here we identify the site of BRCA1-BARD1 required for priming ubiquitin transfer from E2∼ubiquitin and demonstrate that BRCA1-BARD1's ubiquitin ligase activity is required for repositioning 53BP1 on damaged chromatin. We confirm H2A ubiquitination by BRCA1-BARD1 and show that an H2A-ubiquitin fusion protein promotes DNA resection and repair in BARD1-deficient cells. BRCA1-BARD1's function in homologous recombination requires the chromatin remodeler SMARCAD1. SMARCAD1 binding to H2A-ubiquitin and optimal localization to sites of damage and activity in DNA repair requires its ubiquitin-binding CUE domains. SMARCAD1 is required for 53BP1 repositioning, and the need for SMARCAD1 in olaparib or camptothecin resistance is alleviated by 53BP1 loss. Thus, BRCA1-BARD1 ligase activity and subsequent SMARCAD1-dependent chromatin remodeling are critical regulators of DNA repair.
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