The Cks proteins are components of the cyclin-dependent kinase(CDK)/cyclin complexes that regulate mitosis. Thus, Cks proteins play important roles during the cell cycle1. Cks2 belongs to the highly conserved Suc1/Cks family of proteins that can bind to certain CDKs and are required for cell-cycle progression. Cks proteins may regulate the catalytic activity of the cdk2/cyclin A complex, as they have been shown to inhibit the activation of cdk2. The Cks2 gene has been localized to 9q22, which places it close to a putative tumor suppressor locus.