Monopolin is a protein complex that in budding yeast is composed of the four proteins CSM1, HRR25, LRS4, and MAM1. Monopolin is required for the segregation of homologous centromeres to opposite poles of a dividing cell during anaphase I of meiosis. ^[1] This occurs by bridging DSN1 kinetochore proteins to sister kinetochores within the centromere to physically fuse them and allow for the microtubules to pull each homolog toward opposite mitotic spindles. ^[2]

Monopolin is composed of a 4 CSM1:2 LRS4 complex which forms a V-shaped structure with two globular heads at the ends, which are responsible for directly crosslinking sister kinetochores. ^[1] Bound to each CSM1 head is a MAM1 protein which recruits one copy of the HRR25 kinase. ^[3] The hydrophobic cavity on the CSM1 subunit allows the hydrophobic regions of Monopolin receptor and kinetochore protein, DSN1, to bind to and fuse the sister kinetochores. ^[2] Microtubules can then attach to the kinetochores on the homologous centromeres and pull them toward opposite mitotic spindles to complete anaphase of meiosis I.

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