Required for high-fidelity chromosome segregation during the later part of each cell cycle. Acts in opposition to the phosphatase PP1. Has a role in attaching the kinetochores to the microtubules and ensuring that sister kinetochores connect to opposite poles. The promotion of bi-orientation is achieved by selectively detaching kinetochore-microtubule attachments that are not under tension. Phosphorylates histone H3 to form H3S10ph during mitosis and meiosis. Phosphorylates RGD1 in vitro. {ECO:0000269|PubMed:10975519; ECO:0000269|PubMed:11853667; ECO:0000269|PubMed:12408861; ECO:0000269|PubMed:23454383}.