 CDC6 is an ATP binding protein and a member of the pre-replicative complex (pre-RC) together with the origin recognition complex (ORC), Cdt1 and the MCM complex (containing MCM2-7p).CDC6 assembles after ORC in an ATP dependent manner and is required for loading MCM proteins onto the DNA.Reconstruction of electron microscope images showed that the ORC-CDC6 complex forms a ring-shaped structure with similar dimensions to those of ring-shaped MCM helicase.