Human Rad52-mediated homology search and annealing occurs by continuous interactions between overlapping nucleoprotein complexes

摘要

The Rad52 protein has critical functions in distinct pathways of the homology-directed DNA repair, one of which is to promote the annealing of complementary strands of DNA. Both yeast and human Rad52 proteins organize into ring-shaped oligomers with the predominant form being a heptamer. Despite the wealth of information obtained in previous investigations, how Rad52 mediates homology search and annealing remains unclear. Here, we developed single-molecule fluorescence resonance energy transfer approaches to probe hRad52-mediated DNA annealing events in real time. We found that annealing proceeds in successive steps involving rearrangements of the ssDNA–hRad52 complex. Moreover, after initial pairing, further search for extended homology occurs without dissociation. This search process is driven by an interaction between 2 overlapping nucleoprotein complexes. In light of these observations we propose a model for hRad52-mediated DNA annealing where ssDNA release and dsDNA zippering are coordinated through successive rearrangement of overlapping nucleoprotein complexes.