Assessment of the levels of cyclin E, A, and B and their CDK-associated kinase activity in CD34⁺ cells cultured on FN- versus BSA-coated plates. After 48 hours of culture in cytokines on FN- versus BSA-coated plates, cell numbers were equalized and half of the cells were used for subcellular fractionation, immunoblotting for cyclin D3 and CDK6 (A, left), cyclin A and CDK2 (A, right), cyclin E (B, left), cyclin A (B, left), and cyclin B (B, left). The other half of the cells were used for immunoprecipitation with antibodies against specific cyclins (as indicated) followed by in vitro histone H1 kinase assay to assess activity of CDKs associated with cyclin E (A, right), cyclin A (B, right), and cyclin B (B, right).