RB1 and neoplasm: Toward this end, we were drawn to the tumor suppressorP16 protein whose binding sequence to the CDK4/6 contains a helix-turn-helixstructure (Figure S1).19 P16 exerts its tumor-suppressor effect via its action asa CDK4/6 inhibitor that prevents the phosphorylation of retinablastoma(Rb) resulting in G0/G1 cell cycle arrest.