The endoplasmic reticulum takes center stage in cell cycle regulation.

Cell cycle progression is controlled by the action of cyclins and their partners, the cyclin-dependent kinases (CDKs). Although many of the cyclin/CDK targets are in the nucleus, some cyclins spend part of their time in the cytoplasm. Until recently, it was not clear what happens to these cyclins while they are in the cytoplasm; now, two different cyclins have been found to be associated with the endoplasmic reticulum. The question is why.