Fig. (1).

Schematic representation of the DNA replication process. Pre-RC components are recruited to the replication origins in a stepwise manner during late M and early G1 phases of the cell cycle. At the origins, ORC recruits Cdc6 and Cdt1, which in turn are required for the subsequent loading of the Mcm2–7 complex. After pre-RC has assembled, its activation during S phase involves the assembly of a second set of factors like Cdc45 and GINS as well as the activity of Cdk1-Clb5,6, which phosphorylates and determines the fate of specific components of the replication machinery. Origin firing and DNA replication then start bidirectionally (modified from Barberis and Klipp, Genome Inform. 2007).