A POTENT TRANSREPRESSION DOMAIN IN THE RETINOBLASTOMA PROTEIN INDUCESA CELL-CYCLE ARREST WHEN BOUND TO E2F SITES

An intact T/E1A-binding domain (the pocket) is necessary, but not suff icient, for the retinoblastoma protein (RB) to bind to DNA-protein com plexes containing E2F and for RB to induce a G(1)/S block Indirect evi dence suggests that the binding of RB to E2F may, in addition to inhib iting E2F transactivation function, generate a complex capable of func tioning as a transrepressor, Here we show that a chimera in which the E2F1 transactivation domain was replaced with the RB pocket could, in a DNA-binding and pocket-dependent manner, mimic the ability of RB to repress transcription and induce a cell cycle arrest, In contrast, a t ransdominant negative E2F1 mutant that is capable of blocking E2F-depe ndent transactivation did not, Fusion of the RB pocket to a heterologo us DNA-binding domain unrelated to E2F likewise generated a transrepre ssor protein when scored against a suitable reporter, These results su ggest that growth suppression by RB is due, at least in part, to trans repression mediated by the pocket domain bound to certain promoters vi a E2F.