Generation of meiotic crossovers in many eukaryotes requires the elimination of anti-crossover activities by using the Msh4-Msh5 heterodimer to block helicases. Msh4 and Msh5 have been lost from the flies Drosophila and Glossina, but we identified a complex of minichromosome maintenance (MCM) proteins that functionally replace Msh4-Msh5. We found that REC, an ortholog of MCM8 that evolved under strong positive selection in flies, interacts with MEI-217 and MEI-218, which arose from a previously undescribed metazoan-specific MCM protein. Meiotic crossovers were reduced in Drosophila rec, mei-217, and mei-218 mutants; however, removal of the Bloom syndrome helicase (BLM) ortholog restored crossovers. Thus, MCMs were co-opted into a novel complex that replaced the meiotic pro-crossover function of Msh4-Msh5 in flies.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3599781 | PMC |
http://dx.doi.org/10.1126/science.1228190 | DOI Listing |
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