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. 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. Component of the mcm2-7 complex (RLF-M). The complex forms a toroidal hexameric ring with the proposed subunit order mcm2-mcm6-mcm4-mcm7-mcm3-mcm5 (By similarity). Component of the replisome complex (By similarity). Component of the CMG helicase complex, composed of the mcm2-7 complex, the GINS complex and cdc45 (By similarity). Associated with chromatin before the formation of nuclei and detaches from it as DNA replication progresses. May be in a phosphorylated state in the mitotic mcm complex. Phosphorylated in the interphase mcm complex. Phosphorylated by the cdc7-dbf4 and cdc7-dbf4b complexes (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.