Acts as component of the MCM2-7 complex (MCM complex) which is the putative replicative helicase essential for 'once per cell cycle' DNA replication initiation and elongation in eukaryotic cells (PubMed:10567526). The active ATPase sites in the MCM2-7 ring are formed through the interaction surfaces of two neighboring subunits such that a critical structure of a conserved arginine finger motif is provided in trans relative to the ATP-binding site of the Walker A box of the adjacent subunit. The six ATPase active sites, however, are likely to contribute differentially to the complex helicase activity. Required for the entry in S phase and for cell division. Plays a role in terminally differentiated hair cells development of the cochlea and induces cells apoptosis. Component of the MCM2-7 complex. The complex forms a toroidal hexameric ring with the proposed subunit order MCM2-MCM6-MCM4-MCM7-MCM3-MCM5 (By similarity). Interacts with DBF4 (PubMed:10517317). Interacts with KAT7 (PubMed:11278932). May interact with MCM10 (By similarity). Component of the replisome complex composed of at least DONSON, MCM2, MCM7, PCNA and TICRR (By similarity). Component of the CMG helicase complex, composed of the MCM2-7 complex, the GINS complex and CDC45 (By similarity). Forms a co-chaperone complex with DNAJC9 and histone H3.3-H4 heterodimers (By similarity). Within the complex, interacts (via N-terminus) with DNAJC9 (via C-terminus); the interaction is histone-dependent (By similarity). Associated with chromatin before the formation of nuclei and detaches from it as DNA replication progresses. Phosphorylated on Ser-108 by ATR in proliferating cells. Ser-108 proliferation is increased by genotoxic agents. Ser-40 is mediated by the CDC7-DBF4 and CDC7-DBF4B complexes, while Ser-53 phosphorylation is only mediated by the CDC7-DBF4 complex. Phosphorylation by the CDC7-DBF4 complex during G1/S phase is required for the initiation of DNA replication (By similarity). Early fractionation of eukaryotic MCM proteins yielded a variety of dimeric, trimeric and tetrameric complexes with unclear biological significance. Specifically a MCM467 subcomplex is shown to have in vitro helicase activity which is inhibited by the MCM2 subunit. The MCM2-7 hexamer is the proposed physiological active complex. Belongs to the MCM family. Extended N-terminus.