title: The crystal structure of the complex of replication protein A subunits RPA32 and RPA14 reveals a mechanism for single-stranded DNA binding.
abstract: Replication protein A (RPA), the eukaryote single-stranded DNA-binding protein (SSB), is a heterotrimer. The largest subunit, RPA70, which harbours the major DNA-binding activity, has two DNA-binding domains that each adopt an OB-fold. The complex of the two smaller subunits, RPA32 and RPA14, has weak DNA-binding activity but the mechanism of DNA binding is unknown. We have determined the crystal structure of the proteolytic core of RPA32 and RPA14, which consists of the central two-thirds of RPA32 and the entire RPA14 subunit. The structure revealed that RPA14 and the central part of RPA32 are structural homologues. Each subunit contains a central OB-fold domain, which also resembles the DNA-binding domains in RPA70; an N-terminal extension that interacts with the central OB-fold domain; and a C-terminal helix that mediate heterodimerization via a helix-helix interaction. The OB-fold of RPA32, but not RPA14, possesses additional similarity to the RPA70 DNA-binding domains, supporting a DNA-binding role for RPA32. The discovery of a third and fourth OB-fold in RPA suggests that the quaternary structure of SSBs, which in Bacteria and Archaea are also tetramers of OB-folds, is conserved in evolution. The structure also suggests a mechanism for RPA trimer formation.
authors.affiliation: Department of Medical Genetics and Microbiology, University of Toronto, 1 King's College Circle, Toronto, Ontario M5S 1A8.
authors.forename: A
authors.initials: A
authors.lastname: Bochkarev
authors.forename: E
authors.initials: E
authors.lastname: Bochkareva
authors.forename: L
authors.initials: L
authors.lastname: Frappier
authors.forename: A M
authors.initials: AM
authors.lastname: Edwards
mesh_terms: D000595:Amino Acid Sequence; D018360:Crystallography, X-Ray; D004277:DNA, Single-Stranded / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000378:metabolism; D019281:Dimerization; D006801:Humans; D008969:Molecular Sequence Data; D011487:Protein Conformation; D011506:Proteins / Q000737:chemistry / Q000378:metabolism; D012318:RNA Polymerase I; D051716:Replication Protein A; D029701:Saccharomyces cerevisiae Proteins
chemical_list: D004277:DNA, Single-Stranded; D004268:DNA-Binding Proteins; D011506:Proteins; C497167:RPA1 protein, human; C093847:RPA14 protein, S cerevisiae; D051716:Replication Protein A; D029701:Saccharomyces cerevisiae Proteins; D012318:RNA Polymerase I