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. ATP + H2O = ADP + H(+) + phosphate Component of the mcm2-7 complex (RLF-M) (PubMed:8816774, PubMed:16369567, PubMed:7760937, PubMed:7760938, PubMed:9214646, PubMed:9214647, PubMed:9851868). The complex forms a toroidal hexameric ring with the proposed subunit order mcm2-mcm6-mcm4-mcm7-mcm3-mcm5 (PubMed:16369567, PubMed:7760937, PubMed:7760938, PubMed:9214646, PubMed:9214647, PubMed:9851868). The heterodimer of mmcm3/mcm5 interacts with mcm4, mmcm6, mcm7 and weakly with mcm2 (PubMed:16369567, PubMed:7760937, PubMed:7760938, PubMed:9214646, PubMed:9214647, PubMed:9851868). Interacts with mcm7, though this interaction may not be direct, and remains in a complex with mcm7 throughout the cell cycle (PubMed:8816774). Component of the CMG helicase complex, composed of the mcm2-7 complex, the GINS complex and cdc45 (PubMed:30979826, PubMed:30842657). Associated with chromatin before the formation of nuclei and detaches from it as DNA replication progresses. Expressed maternally. Expression decreases suddenly at the gastrula stage. Belongs to the MCM family.