The proliferative role of CDK/cyclin proteins, in general, is mediated through the phosphorylation of the major CDK‐substrate, RB1 (Retinoblastoma) tumor suppressor, and its related proteins RBL1 (p107) and RBL2 (p130) [collectively referred to here as pRB]. Here, RBL1 is linked to retinoblastoma.