Visualization of recombination intermediates produced by RAD52-mediated single-strand annealing

Double-strand breaks (DSBs) occur frequently during DNA replication. They a re also caused by ionizing radiation, chemical damage or as part of the ser ies of programmed events that occur during meiosis. In yeast, DSB repair re quires RAD52, a protein that plays a critical role in homologous recombinat ion. Here we describe the actions of human RAD52 protein in a model system for single-strand annealing (SSA) using tailed (i.e. exonuclease resected) duplex DNA molecules. Purified human RAD52 protein binds resected DSBs and promotes associations between complementary DNA termini. Heteroduplex inter mediates of these recombination reactions have been visualized by electron microscopy, revealing the specific binding of multiple rings of RAD52 to th e resected ter-mini and the formation of large protein complexes at heterod uplex joints formed by RAD52-mediated annealing.