The identity of the DNA helicase(s) involved in eukaryotic DNA replication is 
still a matter of debate, but the mini-chromosome maintenance (MCM) proteins are 
the chief candidate. Six conserved MCM proteins, Mcm2-7, are essential for the 
initiation and elongation stages of DNA replication, contain ATP binding pockets 
and can form a hexameric structure resembling that of known prokaryotic and 
viral helicases. However, biochemical proof of their presumed function has 
remained elusive. Several recent reports confirm that the MCM complex is part of 
the cellular machine responsible for the unwinding of DNA during S phase. In one 
of these reports, the helicase activity of Mcm2-7 is finally revealed, when they 
are purified in association with two partners: initiation factor Cdc45 and a 
four-subunit complex called GINS. The Cdc45-MCM-GINS complex could constitute 
the core of a larger macromolecular structure that has been termed the 
"replisome progression complex".