Part of the MIS12 complex; which is required for kinetochore formation and spindle checkpoint activity. Required to target ZW10 to the kinetochore at prometaphase. {ECO:0000269|PubMed:15094189; ECO:0000269|PubMed:15485811; ECO:0000269|PubMed:15824131; ECO:0000269|PubMed:16732327}.