The human Rad52 protein exists as a heptameric ring.
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.
Stasiak
A Z
AZ
Laboratory of Ultrastructural Analysis, University of Lausanne, Lausanne, CH-1015, Switzerland.
Larquet
E
E
Stasiak
A
A
Müller
S
S
Engel
A
A
Van Dyck
E
E
West
S C
SC
Egelman
E H
EH
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
D004268:DNA-Binding Proteins; C497194:RAD52 protein, human; D051721:Rad52 DNA Repair and Recombination Protein; D011993:Recombinant Fusion Proteins