title: Human XPA and RPA DNA repair proteins participate in specific recognition of triplex-induced helical distortions.
abstract: Nucleotide excision repair (NER) plays a central role in maintaining genomic integrity by detecting and repairing a wide variety of DNA lesions. Xeroderma pigmentosum complementation group A protein (XPA) is an essential component of the repair machinery, and it is thought to be involved in the initial step as a DNA damage recognition and/or confirmation factor. Human replication protein A (RPA) and XPA have been reported to interact to form a DNA damage recognition complex with greater specificity for damaged DNA than XPA alone. The mechanism by which these two proteins recognize such a wide array of structures resulting from different types of DNA damage is not known. One possibility is that they recognize a common feature of the lesions, such as distortions of the helical backbone. We have tested this idea by determining whether human XPA and RPA proteins can recognize the helical distortions induced by a DNA triple helix, a noncanonical DNA structure that has been shown to induce DNA repair, mutagenesis, and recombination. We measured binding of XPA and RPA, together or separately, to substrates containing triplexes with three, two, or no strands covalently linked by psoralen conjugation and photoaddition. We found that RPA alone recognizes all covalent triplex structures, but also forms multivalent nonspecific DNA aggregates at higher concentrations. XPA by itself does not recognize the substrates, but it binds them in the presence of RPA. Addition of XPA decreases the nonspecific DNA aggregate formation. These results support the hypothesis that the NER machinery is targeted to helical distortions and demonstrate that RPA can recognize damaged DNA even without XPA.
authors.affiliation: Department of Carcinogenesis, University of Texas M. D. Anderson Cancer Center, Science Park-Research Division, Park Road 1-C, Smithville, TX 78957, USA. kvasquez@sprd1.mdacc.tmc.edu
authors.forename: Karen M
authors.initials: KM
authors.lastname: Vasquez
authors.forename: Jesper
authors.initials: J
authors.lastname: Christensen
authors.forename: Lei
authors.initials: L
authors.lastname: Li
authors.forename: Rick A
authors.initials: RA
authors.lastname: Finch
authors.forename: Peter M
authors.initials: PM
authors.lastname: Glazer
mesh_terms: D001483:Base Sequence; D001665:Binding Sites; D004247:DNA / Q000378:metabolism; D004249:DNA Damage; D017931:DNA Primers / Q000494:pharmacology; D004260:DNA Repair; D004268:DNA-Binding Proteins / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D004797:Enzyme-Linked Immunosorbent Assay; D005363:Ficusin / Q000737:chemistry; D006801:Humans; D007438:Introns; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D011485:Protein Binding; D011995:Recombination, Genetic; D051716:Replication Protein A; D014466:Ultraviolet Rays; D051760:Xeroderma Pigmentosum Group A Protein
chemical_list: D017931:DNA Primers; D004268:DNA-Binding Proteins; C497167:RPA1 protein, human; D051716:Replication Protein A; C497314:XPA protein, human; D051760:Xeroderma Pigmentosum Group A Protein; C051802:triplex DNA; D004247:DNA; D005363:Ficusin