ABSTRACT
Saccharomyces cerevisiae Rad52 protein promotes homologous recombination by nucleating the Rad51 recombinase onto replication protein A-coated single-stranded DNA strands and also by directly annealing such strands. We show that the purified rad52-R70A mutant protein, with a compromised amino-terminal DNA binding domain, is capable of Rad51 delivery to DNA but is deficient in DNA annealing. Results from chromatin immunoprecipitation experiments find that rad52-R70A associates with DNA double-strand breaks and promotes recruitment of Rad51 as efficiently as wild-type Rad52. Analysis of gene conversion intermediates reveals that rad52-R70A cells can mediate DNA strand invasion but are unable to complete the recombination event. These results provide evidence that DNA binding by the evolutionarily conserved amino terminus of Rad52 is needed for the capture of the second DNA end during homologous recombination.
Subject(s)
DNA Repair , Rad52 DNA Repair and Recombination Protein/metabolism , Recombination, Genetic , Saccharomyces cerevisiae Proteins/metabolism , Amino Acid Substitution , Binding Sites , Chromatin Immunoprecipitation , DNA Breaks, Double-Stranded , DNA, Single-Stranded , Electrophoresis, Polyacrylamide Gel , Microscopy, Electron , Mutation , Protein Binding , Rad51 Recombinase/genetics , Rad51 Recombinase/metabolism , Rad52 DNA Repair and Recombination Protein/chemistry , Rad52 DNA Repair and Recombination Protein/genetics , Saccharomyces cerevisiae/genetics , Saccharomyces cerevisiae/metabolism , Saccharomyces cerevisiae Proteins/chemistry , Saccharomyces cerevisiae Proteins/geneticsABSTRACT
Homologous recombination (HR) is a major DNA repair pathway and therefore essential for maintaining the integrity of the genome. HR is catalyzed by proteins encoded by genes of the RAD52 epistasis group, including the recombinase Rad51 and its mediator Rad52. HR proteins fused with green fluorescent protein form foci at damaged DNA reflecting the assembly of repair centers that harbor a high concentration of repair proteins. Rad52 mediates the recruitment of Rad51 and other HR proteins to DNA damage. To understand the mechanism for the assembly of Rad52-dependent DNA repair centers, we used a mutational strategy to identify a Rad52 domain essential for its recruitment to DNA repair foci. We present evidence to implicate an acidic domain in Rad52 in DNA repair focus formation. Mutations in this domain confer marked DNA damage sensitivity and recombination deficiency. Importantly, these Rad52 mutants are specifically compromised for interaction with the single-stranded DNA-binding factor RPA. Based on these findings, we propose a model where Rad52 displaces RPA from single-stranded DNA using the acidic domain as a molecular lever.
Subject(s)
DNA Repair , Rad52 DNA Repair and Recombination Protein/metabolism , Saccharomyces cerevisiae/metabolism , Amino Acid Sequence , DNA Damage , Epistasis, Genetic , Microscopy, Fluorescence , Models, Biological , Molecular Sequence Data , Mutation , Protein Binding , Rad51 Recombinase/metabolism , Rad52 DNA Repair and Recombination Protein/chemistry , Recombination, Genetic , Sequence Homology, Amino Acid , Two-Hybrid System TechniquesABSTRACT
Rad52 is essential for all homologous recombination and DNA double strand break repair events in Saccharomyces cerevisiae. This protein is multifunctional and contains several domains that allow it to interact with DNA as well as with different repair proteins. However, it has been unclear how Rad52 enters the nucleus. In the present study, we have used a combination of mutagenesis and sequence analysis to show that Rad52 from S. cerevisiae contains a single functional pat7 type NLS essential for its nuclear localization. The region containing the NLS seems only to be involved in nuclear transport as it plays no role in repair of MMS-induced DNA damage. The NLS in Rad52 is weak, as monomeric protein species that harbor this NLS are mainly located in the cytosol. In contrast, multimeric protein complexes wherein each subunit contains a single NLS(Rad52) sort efficiently to the nucleus. Based on the results we propose a model where the additive effect of multiple NLS(Rad52) sequences in a Rad52 ring-structure ensures efficient nuclear localization of Rad52.
