title: Site-specific repair of cyclobutane pyrimidine dimers in a positioned nucleosome by photolyase and T4 endonuclease V in vitro.
abstract: Since genomic DNA is folded into nucleosomes, and DNA damage is generated all over the genome, a central question is how DNA repair enzymes access DNA lesions and how they cope with nucleosomes. To investigate this topic, we used a reconstituted nucleosome (HISAT nucleosome) as a substrate to generate DNA lesions by UV light (cyclobutane pyrimidine dimers, CPDs), and DNA photolyase and T4 endonuclease V (T4-endoV) as repair enzymes. The HISAT nucleosome is positioned precisely and contains a long polypyrimidine region which allows one to monitor formation and repair of CPDs over three helical turns. Repair by photolyase and T4-endoV was inefficient in nucleosomes compared with repair in naked DNA. However, both enzymes showed a pronounced site-specific modulation of repair on the nucleosome surface. Removal of the histone tails did not substantially enhance repair efficiency nor alter the site specificity of repair. Although photolyase and T4-endoV are different enzymes with different mechanisms, they exhibited a similar site specificity in nucleosomes. This implies that the nucleosome structure has a decisive role in DNA repair by exerting a strong constraint on damage accessibility. These findings may serve as a model for damage recognition and repair by more complex repair mechanisms in chromatin.
authors.affiliation: Institut für Zellbiologie, ETH-Zürich, Hönggerberg, CH-8093 Zürich, Switzerland.
authors.forename: U
authors.initials: U
authors.lastname: Schieferstein
authors.forename: F
authors.initials: F
authors.lastname: Thoma
mesh_terms: D004247:DNA / Q000528:radiation effects; D004260:DNA Repair; D004255:Deoxyribodipyrimidine Photo-Lyase / Q000378:metabolism*; D043224:Deoxyribonuclease (Pyrimidine Dimer); D004706:Endodeoxyribonucleases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D006657:Histones / Q000378:metabolism; D009707:Nucleosomes / Q000378:metabolism*; D011740:Pyrimidine Dimers / Q000235:genetics*; D014466:Ultraviolet Rays; D014764:Viral Proteins
chemical_list: D006657:Histones; D009707:Nucleosomes; D011740:Pyrimidine Dimers; D014764:Viral Proteins; D004247:DNA; D004706:Endodeoxyribonucleases; C470698:endonuclease V, phage T4; D043224:Deoxyribonuclease (Pyrimidine Dimer); D004255:Deoxyribodipyrimidine Photo-Lyase