Exonuclease 1

[8] It is similar to the Saccharomyces cerevisiae protein Exo1 which interacts with Msh2 and which is involved in DNA mismatch repair and homologous recombination.

[7] ExoI is essential for meiotic progression through metaphase I in the budding yeast Saccharomyces cerevisiae and in mouse.

[9][10] Recombination during meiosis is often initiated by a DNA double-strand break (DSB) as illustrated in the accompanying diagram.

Later in the recombination process, Exo1 acts to facilitate the resolution of DHJs into COs, independently of its nuclease activities.

In resolving DHJs, Exo 1 acts together with MLH1-MLH3 heterodimer (MutL gamma) and Sgs1 (ortholog of Bloom syndrome helicase) to define a joint molecule resolution pathway that produces the majority of crossovers.

A current model of meiotic recombination, initiated by a double-strand break or gap, followed by pairing with an homologous chromosome and strand invasion to initiate the recombinational repair process. Repair of the gap can lead to crossover (CO) or non-crossover (NCO) of the flanking regions. CO recombination is thought to occur by the Double Holliday Junction (DHJ) model, illustrated on the right, above. NCO recombinants are thought to occur primarily by the Synthesis Dependent Strand Annealing (SDSA) model, illustrated on the left, above. Most recombination events appear to be the SDSA type.