Required for both DNA replication and mitosis. DNA replication licensing factor, required for pre-replication complex assembly. Cooperates with CDC6 and the origin recognition complex (ORC) during G1 phase of the cell cycle to promote the loading of the mini-chromosome maintenance (MCM) complex onto DNA to generate pre-replication complexes (pre-RC). Required also for mitosis by promoting stable kinetochore-microtubule attachments (By similarity). Potential oncogene (PubMed:11850834).