The repair of DNA damage by homologous recombination (HR) is a key pathway for the maintenance of genetic stability in mammalian cells, especially during and following DNA replication. The central HR protein is RAD51, which ensures high fidelity DNA repair by facilitating strand exchange between damaged and undamaged homologous DNA segments. Several RAD51-like proteins, including XRCC2, appear to help with this process, but their roles are not well understood. Here we show that XRCC2 is highly conserved and that most substantial truncations of the protein destroy its ability to function. XRCC2 and its partner protein RAD51L3 are found to interact with RAD51 in the 2-hybrid system, and XRCC2 is shown to be important but not essential for the accumulation of RAD51 at the sites of DNA damage. We visualize the localization of XRCC2 protein at the same sites of DNA damage for the first time using specialized irradiation conditions. Our data indicate that an important function of XRCC2 is to enhance the activity of RAD51, so that the loss of XRCC2 results in a severe delay in the early response of RAD51 to DNA damage.
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