Figure 3.

Cyclin E promotes prereplication complex assembly after cells are released from quiescence, whereas cyclin A initiates DNA synthesis but inhibits assembly of any further prereplication complexes once DNA synthesis has started. (a) Replication of G1 nuclei in G1 cytosol when cyclin CDK complexes are added sequentially to the incubation. (i) and (ii) show the microscope images obtained from the first and third bars of the histogram. Unreplicated nuclei are stained red; replicated nuclei are stained both red and green and thus appear yellow. (b) Summary scheme of the different roles of cyclin E-Cdk2 and cyclin A-Cdk2 in the control of DNA synthesis as cells re-enter the cell cycle from quiescence. Reproduced with permission from Coverley et al. (2002).