Fig. 6.4.

The meiotic recombination pathway in C. elegans. Here one homolog is depicted in black and the other is shown in red. Meiotic recombination is initiated by formation of DSBs. The topoisomerase-like enzyme SPO-11 catalyzes the cleavage of the double-stranded DNA of one sister chromatid. Both 5′ ends of the DSB are rapidly resected by MRE-11, RAD-50, and COM-1 to reveal 3′ single-stranded tails, on which RAD-51 forms a filament. RAD-54 promotes invasion by one end of the DSB into the DNA duplex of the homolog to form the nascent D-loop structure. As DNA synthesis occurs, the D-loop expands. The D-loop structure is processed by two major pathways to yield COs and NCOs. COs, which hold bivalents together, arise from the formation of stable single-end invasions, followed by second end capture and then the formation of double Holliday junctions, which are cleaved by a currently unknown resolvase. NCOs arise from either processing of double Holliday junctions or the synthesis-dependent strand-annealing pathway, through which the invading end of the DSB is ejected so that it can anneal with its sister chromatid. Following annealing, DNA synthesis and ligation occur to complete the formation of NCOs