Fig. 1. Known and hypothetical controls linking the cell cycle and chromatin modification. The controls of the G1-S phase transition of the cell cycle (blue circles) regulate DNA methylation and histone modifications (dark-purple hexagons), which also regulate eachother. Nucleosome assembly (green) onto newly replicated DNA at the replication fork is depicted. DNA methylation (light-purple hexagon) is replicated in a semi-conservative manner. Whether histone modifications are transmitted through cell division in a semi-conservative manner remains a matter of debate. During the S phase, replication-coupled histone replacement (orange box) is likely to play a role in chromatin dynamics. The G2-M transition is also correlated with histone modifications. During the G2 and G1 phases, non-replicative histone replacement (orange box) might play a role in chromatin dynamics, which could be important for the decision whether to enter a new replication cycle or to differentiate.