A new gene family involved in cell cycle regulation was discovered. This family has been termed activators of cyclin-dependent kinases (ACDKs). A number of ACDK genes have been cloned and sequenced. Proteins encoded by ACDK genes specifically were shown to interact with CDKs and pRb, and to upregulate the kinase activity of a CDK using pRb as a substrate. Progression of a cell through the cell cycle can be regulated by modulating ACDK expression in the cell.