Required for high-fidelity chromosome segregation during the later part of each cell cycle in association with the protein kinase IPL1. Stimulates IPL1 kinase activity and facilitates its association with the mitotic spindle. Has a role in attaching the kinetochores to the microtubules and ensuring that sister kinetochores connect to opposite poles. {ECO:0000269|PubMed:10385519; ECO:0000269|PubMed:11724818; ECO:0000269|PubMed:11853667}.