To identify targets through which Cdk2 executes its functions in DNA damage responses, we labeled proteins in whole-cell extracts of wild-type RPE-hTERT and HCT116 human colon carcinoma cells with purified Cdk2as/cyclin A and the analog substrate [γ-32P]N6-(benzyl)-ATP [32], [33]. Here, CDK2 is linked to colon carcinoma.