The retinoblastoma protein (RB) binds to a variety of cellular proteins and suppresses eelMar growth. Such interactions are re

that is inactivated by deletion or by a small mutation of its gene in a variety of cancer cells, including retinoblastoma, osteosarcoma, small-cell lung cancer and bladder cancer (reviewed in Ref. 1). RB has the ability to suppress cell pro- liferation, and this activity is controlled by its cell-cycledependent phosphoryl- ation2? it has been shown th growth-suppressing activity of mainly exerted by binding and ing the traKlscri~tion factor E2F (for re- views, see Refs 4-6). Howe studies have demonstrated functions of RR through the other cellular proteins. In time, much attention has be for the cell~yc~~l~~e~~d~nt ~~os~horyl- atfon of RB. Since the discovery of proteins that Inhibit mammalian Gl~yclin~epende kinases in 1993 (reviewed in Ref. ‘7) much work has linked RB kinases to the control of passage through the restric- tion polnt in late Cl, Functional differ- ences between several RB kinases have also been demonstrated. Here,