Figure 1.

Proteins involved in DSB repair in vertebrate cells. During NHEJ the DNA-PK complex, which consists of the Ku70/Ku80 heterodimer and the DNA-PK catalytic subunit, binds the broken ends and facilitates rejoining by DNA ligase IV and XRCC4. HR is carried out by proteins in the Rad52 epistasis group. These include Rad51, Rad52, Rad54 and the Rad51 paralogs Rad51B, Rad51C, Rad51D, XRCC2, XRCC3, Rad50, Mre11 and Nbs1. During the repair process, Rad51 aided by other accessory factors catalyzes strand exchange with a homologous DNA molecule. The Rad50/Mre11/Nbs1 complex, which has nuclease and DNA-unwinding activities, participates in both HR and NHEJ in ways that are still not fully understood.