Figure 1. Steps in homologous recombination. A DNA double-strand break is formed and processed by an exonuclease to yield single-strand DNA tails that bear a terminal 3¢-hydroxyl group. These single-strand tails are bound by Rad51 and other recombination factors to form a higher order nucleoprotein complex, which has the ability to locate a DNA homologue and catalyses the invasion of the homologue to form a D-loop structure. DNA synthesis replaces the genetic information eliminated during end-processing of the break, and resolution of the subsequent DNA intermediates followed by ligation of the remaining DNA nicks complete the process.

Figure 2. Steps in the formation of a DNA joint. DNA homology search (step I) is effected by reiterative binding and release of the duplex (in blue) by the nucleoprotein complex consisting of single-strand DNA (in black) and recombination proteins (in circles). Once DNA homology is located, alignment of the recombining DNA molecules occurs (step II), followed by DNA strand invasion to form a short DNA joint (step III). The length of the DNA joint is extended by a process called branch migration (step IV).