title: The human Rad52 protein exists as a heptameric ring.
abstract: The RAD52 epistasis group was identified in yeast as a group of genes required to repair DNA damaged by ionizing radiation [1]. Genetic evidence indicates that Rad52 functions in Rad51-dependent and Rad51-independent recombination pathways [2] [3] [4]. Consistent with this, purified yeast and human Rad52 proteins have been shown to promote single-strand DNA annealing [5] [6] [7] and to stimulate Rad51-mediated homologous pairing [8] [9] [10] [11]. Electron microscopic examinations of the yeast [12] and human [13] Rad52 proteins have revealed their assembly into ring-like structures in vitro. Using both conventional transmission electron microscopy and scanning transmission electron microscopy (STEM), we found that the human Rad52 protein forms heptameric rings. A three-dimensional (3D) reconstruction revealed that the heptamer has a large central channel. Like the hexameric helicases such as Escherichia coli DnaB [14] [15], bacteriophage T7 gp4b [16] [17], simian virus 40 (SV40) large T antigen [18] and papilloma virus E1 [19], the Rad52 rings show a distinctly chiral arrangement of subunits. Thus, the structures formed by the hexameric helicases may be a more general property of other proteins involved in DNA metabolism, including those, such as Rad52, that do not bind and hydrolyze ATP.
authors.affiliation: Laboratory of Ultrastructural Analysis, University of Lausanne, Lausanne, CH-1015, Switzerland.
authors.forename: A Z
authors.initials: AZ
authors.lastname: Stasiak
authors.forename: E
authors.initials: E
authors.lastname: Larquet
authors.forename: A
authors.initials: A
authors.lastname: Stasiak
authors.forename: S
authors.initials: S
authors.lastname: Müller
authors.forename: A
authors.initials: A
authors.lastname: Engel
authors.forename: E
authors.initials: E
authors.lastname: Van Dyck
authors.forename: S C
authors.initials: SC
authors.lastname: West
authors.forename: E H
authors.initials: EH
authors.lastname: Egelman
mesh_terms: D000818:Animals; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000648:ultrastructure*; D006801:Humans; D051721:Rad52 DNA Repair and Recombination Protein; D011993:Recombinant Fusion Proteins / Q000648:ultrastructure
chemical_list: D004268:DNA-Binding Proteins; C497194:RAD52 protein, human; D051721:Rad52 DNA Repair and Recombination Protein; D011993:Recombinant Fusion Proteins