Functional and structural basis for a bacteriophage homolog of human RAD52.
In eukaryotes, homologous recombination proteins such as RAD51 and RAD52 play crucial roles in DNA repair and genome stability. Human RAD52 is a member of a large single-strand annealing protein (SSAP) family [1] and stimulates Rad51-dependent recombination [2, 3]. In prokaryotes and phages, it has been difficult to establish the presence of RAD52 homologs with conserved sequences. Putative SSAPs were recently found in several phages that infect strains of Lactococcus lactis[4]. One of these SSAPs was identified as Sak and was found in the virulent L. lactis phage ul36, which belongs to the Siphoviridae family [4, 5]. In this study, we show that Sak is homologous to the N terminus of human RAD52. Purified Sak binds single-stranded DNA (ssDNA) preferentially over double-stranded DNA (dsDNA) and promotes the renaturation of long complementary ssDNAs. Sak also binds RecA and stimulates homologous recombination reactions. Mutations shown to modulate RAD52 DNA binding [6] affect Sak similarly. Remarkably, electron-microscopic reconstruction of Sak reveals an undecameric (11) subunit ring, similar to the crystal structure of the N-terminal fragment of human RAD52 [7, 8]. For the first time, we propose a viral homolog of RAD52 at the amino acid, phylogenic, functional, and structural levels.
Ploquin
Mickaël
M
Genome Stability Laboratory, Laval University Cancer Research Center, Hôtel-Dieu de Québec, 9 McMahon, Québec City G1R 2J6, Canada.
Bransi
Ali
A
Paquet
Eric R
ER
Stasiak
Alicja Z
AZ
Stasiak
Andrzej
A
Yu
Xiong
X
Cieslinska
Anna M
AM
Egelman
Edward H
EH
Moineau
Sylvain
S
Masson
Jean-Yves
JY
D000595:Amino Acid Sequence; D004260:DNA Repair; D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000502:physiology / Q000648:ultrastructure; D006801:Humans; D013294:Lactococcus lactis / Q000821:virology; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010802:Phylogeny; D051721:Rad52 DNA Repair and Recombination Protein / Q000737:chemistry* / Q000502:physiology; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D017906:Siphoviridae / Q000235:genetics*; D040681:Structural Homology, Protein; D014764:Viral Proteins / Q000737:chemistry* / Q000502:physiology / Q000648:ultrastructure
D004268:DNA-Binding Proteins; C497194:RAD52 protein, human; D051721:Rad52 DNA Repair and Recombination Protein; D014764:Viral Proteins