Acts as a component of the MCM2-7 complex (MCM complex) which is the replicative helicase essential for 'once per cell cycle' DNA replication initiation and elongation in eukaryotic cells. Core component of CDC45-MCM-GINS (CMG) helicase, the molecular machine that unwinds template DNA during replication, and around which the replisome is built (PubMed:16899510, PubMed:25661590, PubMed:32453425, PubMed:34694004, PubMed:34700328, PubMed:35585232, PubMed:9305914). 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 (PubMed:16899510, PubMed:25661590, PubMed:32453425, PubMed:9305914). {ECO:0000269|PubMed:16899510, ECO:0000269|PubMed:25661590, ECO:0000269|PubMed:32453425, ECO:0000269|PubMed:34694004, ECO:0000269|PubMed:34700328, ECO:0000269|PubMed:35585232, ECO:0000269|PubMed:9305914}. This is the function of ENSG00000104738 (MCM4, minichromosome maintenance complex component 4).