Fig. 9. Degree of phosphorylation of pRb in p21 and control-transfected cells. The mock-transfected K562 clone M3 was transfected with control vector (C) or the cDNA for p21, respectively, as described in "Materials and Methods." K562/ptsp53/A5 cells transiently transfected with control vector (C) and incubated 24 h at the temperature that is permissive (i.e., 32°C) or nonpermissive (i.e., 37°C) for wild-type p53 activity serve as a positive control for induction of pRb hypophosphorylation. Seventy-two h after transfection, cells were subjected to analysis of pRb by IP-Western blot. Arrow to the right, position of pRb. Left, positions of molecular weight standards. One representative experiment of three performed is shown.