sentences:  Loading of Mcm proteins can only occur during the G1 of the cell cycle, and the loaded complex is then activated during S phase by recruitment of the Cdc45 protein and the GINS complex to form the active Cdc45–Mcm–GINS (CMG) helicase at DNA replication forks.Mcm activity is required throughout the S phase for DNA replication.A variety of regulatory factors assemble around the CMG helicase to produce the ‘Replisome Progression Complex’ which associates with DNA polymerases to form the eukaryotic replisome, the structure of which is still quite poorly defined in comparison with its bacterial counterpart.