The Human Ligase IIIα-XRCC1 Protein Complex Performs DNA Nick Repair after Transient Unwrapping of Nucleosomal DNA.
Reactive oxygen species generate potentially cytotoxic and mutagenic lesions in DNA, both between and within the nucleosomes that package DNA in chromatin. The vast majority of these lesions are subject to base excision repair (BER). Enzymes that catalyze the first three steps in BER can act at many sites in nucleosomes without the aid of chromatin-remodeling agents and without irreversibly disrupting the host nucleosome. Here we show that the same is true for a protein complex comprising DNA ligase IIIα and the scaffolding protein X-ray repair cross-complementing protein 1 (XRCC1), which completes the fourth and final step in (short-patch) BER. Usingin vitroassembled nucleosomes containing discretely positioned DNA nicks, our evidence indicates that the ligase IIIα-XRCC1 complex binds to DNA nicks in nucleosomes only when they are exposed by periodic, spontaneous partial unwrapping of DNA from the histone octamer; that the scaffolding protein XRCC1 enhances the ligation; that the ligation occurs within a complex that ligase IIIα-XRCC1 forms with the host nucleosome; and that the ligase IIIα-XRCC1-nucleosome complex decays when ligation is complete, allowing the host nucleosome to return to its native configuration. Taken together, our results illustrate ways in which dynamic properties intrinsic to nucleosomes may contribute to the discovery and efficient repair of base damage in chromatin.
From the Department of Microbiology and Molecular Genetics, University of Vermont, Burlington, Vermont 05405 and.
Wendy J
0000-0002-7629-8611
WJ
Cannan
the University of New Mexico Cancer Center and Departments of Internal Medicine and Molecular Genetics and Microbiology, University of New Mexico, Albuquerque, New Mexico 87131.
Ishtiaque
I
Rashid
the University of New Mexico Cancer Center and Departments of Internal Medicine and Molecular Genetics and Microbiology, University of New Mexico, Albuquerque, New Mexico 87131.
Alan E
AE
Tomkinson
From the Department of Microbiology and Molecular Genetics, University of Vermont, Burlington, Vermont 05405 and.
Susan S
0000-0002-3906-0321
SS
Wallace
From the Department of Microbiology and Molecular Genetics, University of Vermont, Burlington, Vermont 05405 and david.pederson@uvm.edu.
David S
DS
Pederson
D001665:Binding Sites; D002843:Chromatin; D004247:DNA / Q000378:metabolism*; D000072481:DNA Ligase ATP; D011088:DNA Ligases / Q000378:metabolism* / Q000502:physiology; D004260:DNA Repair / Q000502:physiology*; D004268:DNA-Binding Proteins / Q000378:metabolism* / Q000502:physiology; D006657:Histones / Q000378:metabolism; D006801:Humans; D009707:Nucleosomes / Q000235:genetics*; D000076105:X-ray Repair Cross Complementing Protein 1
D002843:Chromatin; D004268:DNA-Binding Proteins; D006657:Histones; D009707:Nucleosomes; D000076105:X-ray Repair Cross Complementing Protein 1; D004247:DNA; D011088:DNA Ligases; D000072481:DNA Ligase ATP
DNA enzyme; DNA repair; base excision repair (BER); chromatin; histone