Has a dual function in spindle-assembly checkpoint signaling and in promoting the establishment of correct kinetochore-microtubule (K-MT) attachments. Plays a role in the kinetochore-mediated mitotic checkpoint; which delays anaphase onset until all chromosomes have attached properly to the mitotic spindle. Required to establish and maintain spindle checkpoint arrest in eggs. {ECO:0000269|PubMed:12538762}.