MCM helicase is a hexameric protein complex composed of six subunits: MCM2, MCM3, MCM4, MCM5, MCM6, and MCM7. It functions as an ATP-dependent enzyme, unwinding the DNA double helix to provide single-stranded DNA templates necessary for replication. The complex is loaded onto DNA during the G1 phase of the cell cycle and becomes active in the S phase, ensuring that DNA replication occurs once and only once per cell cycle.
