Complex formation by the human RAD51C and XRCC3 recombination repair proteins

In vertebrates, the RAD51 protein is required for genetic recombination, DN A repair, and cellular proliferation. Five paralogs of RAD51, known as RAD5 1B, RAD51C, RAD51D, XRCC2, and XRCC3, have been identified and also shown t o be required for recombination and genome stability. At the present time, however, very little is known about their biochemical properties or precise biological functions. As a first step toward understanding the roles of th e RAD51 paralogs in recombination, the human RAD51C and XRCC3 proteins were overexpressed and purified from baculovirus-infected insect cells. The two proteins copurify as a complex, a property that reflects their endogenous association observed in HeLa cells. Purified RAD51C-XRCC3 complex binds sin gle-stranded, but not duplex DNA, to form protein-DNA networks that have be en visualized by electron microscopy.