sentences:  The levels and activity of Cdc6 regulate the frequency with which the origins of replication are utilized during the cell cycle.The chromatin licensing and DNA replication factor 1 (Cdt1) protein is required for the licensing of chromatin for DNA replication.In "S. cerevisiae", Cdt1 facilitates the loading of the Mcm2-7 complex one at a time onto the chromosome by stabilising the left-handed open-ring structure of the Mcm2-7 single hexamer.