Promotes progression through the cell cycle via binding and activation of CDK1 and CDK2. Involved in the spindle-assembly checkpoint. Required for recruitment of MAD2L1, BUBR1 and BUB1 to kinetochores. Required for the correct localization of the active form of Aurora B in prometaphase. {ECO:0000269|PubMed:15611625, ECO:0000269|PubMed:20605920}. This is the function of Ensembl gene identifier ENSG00000204710 (SPDYC, speedy/RINGO cell cycle regulator family member C).