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. The existence of maternal and zygotic forms of mcm3 and mcm6 suggests that specific forms of mcm2-7 complexes may be used during different stages of development (By similarity). ATP + H2O = ADP + H(+) + phosphate 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. The heterodimer of mmcm3/mcm5 interacts with mcm4, mmcm6, mcm7 and weakly with mcm2. The N-terminus is required for interaction with mmcm3, though this interaction may not be direct, and remains in a complex with mmcm3 throughout the cell cycle. Begins to associate with zmcm6 at the neurula stage (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. Ubiquitinated by traip when forks converge following formation of DNA interstrand cross-links. Short ubiquitin chains on mcm7 promote recruitment of DNA glycosylase neil3. If the interstrand cross-link cannot be cleaved by neil3, the ubiquitin chains continue to grow on mcm7, promoting the unloading of the CMG helicase complex by the vcp/p97 ATPase. 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.