A Single-Strand Annealing Protein Clamps DNA to Detect and Secure Homology.

ABSTRACT: Repair of DNA breaks by single-strand annealing (SSA) is a major mechanism for the maintenance of genomic integrity. SSA is promoted by proteins (single-strand-annealing proteins [SSAPs]), such as eukaryotic RAD52 and ? phage Red?. These proteins use a short single-stranded region to find sequence identity and initiate homologous recombination. However, it is unclear how SSAPs detect homology and catalyze annealing. Using single-molecule experiments, we provide evidence that homology is recognized by Red? monomers that weakly hold single DNA strands together. Once annealing begins, dimerization of Red? clamps the double-stranded region and nucleates nucleoprotein filament growth. In this manner, DNA clamping ensures and secures a successful detection for DNA sequence homology. The clamp is characterized by a structural change of Red? and a remarkable stability against force up to 200 pN. Our findings not only present a detailed explanation for SSAP action but also identify the DNA clamp as a very stable, noncovalent, DNA-protein interaction.

SUBMITTER: Ander M 

PROVIDER: S-EPMC4535883 | biostudies-literature | 2015 Aug

REPOSITORIES: biostudies-literature