Csm1p

Csm1p is a meiosis-specific kinetochore-associated protein in the budding yeast Saccharomyces cerevisiae, encoded by the CSM1 gene. It is a core component of the monopolin complex, which also includes Lrs4p and, during meiosis I, Mam1p. The complex functions to co-orient sister chromatids at the centromere, promoting their attachment to a single spindle pole and enabling the reductional division that characterizes meiosis I.

Function and role

Csm1p participates in establishing monopolar kinetochore attachments during meiosis I, thereby ensuring that sister chromatids are directed to the same pole while homologs are segregated to opposite poles. This mechanism stabilizes chromosome segregation and reduces missegregation errors. In cells lacking Csm1p, chromosome missegregation increases and sporulation efficiency declines, reflecting its essential role in meiotic chromosome dynamics.

Localization and interactions

Csm1p localizes to centromeric regions during meiosis I and interacts with Lrs4p to form the core monopolin dimer, which then associates with Mam1p to complete the monopolin complex. These interactions coordinate centromeric cohesion changes and kinetochore attachments necessary for proper chromosome disjunction.

Structure and conservation

Csm1p is thought to contain coiled-coil regions that enable stable interactions with Lrs4p and Mam1p, facilitating complex formation. The monopolin function is conserved in budding yeast and related species, though the specific regulatory details can vary between organisms.

Related topics

Csm1p is a component of the monopolin complex, which also involves Lrs4p and Mam1p, and plays a critical role in meiosis I chromosome segregation.