May be involved in the initiation of DNA replication. May play a role in endoreduplication. Could act as one of the factors that contributes to maintain endoreduplication competence. Highly expressed in roots, flower buds and etiolated seedlings. Expressed in leaves and stems (PubMed:11604464). Highly expressed in proliferating cells such as root meristems, leaf primordia and young growing leaves, as well as cells undergoing endoreduplication cycles (PubMed:11752380). Cell cycle regulated. Up-regulated at the G1/S phase transition and then decreases rapidly as cells progress into S-phase (PubMed:11752380, PubMed:11669580). Degraded in a proteasome-dependent manner in proliferating cells, but not in endoreduplicating cells (PubMed:11752380). Cells expressing ectopically CDC6 have increased levels of endopolyploidy. Belongs to the CDC6/cdc18 family.