CHARACTERIZATION OF THE RETINOBLASTOMA BINDING-PROTEINS RBP1 AND RBP2

The retinoblastoma gene product, pRB, regulates cell proliferation by binding to and inhibiting the activity of key growth promoting protein s. Several cellular proteins have been shown to bind directly to pRB a nd the genes encoding a number of them have been isolated. The protein product of one of these genes is the transcription factor E2F. We hav e now isolated cDNA clones that contain the full-length coding sequenc e of two other proteins, RBP1 and RBP2, cloned originally by their int eraction with pRB. The products of the RBP1 and RBP2 genes are ubiquot osly expressed, large (200 kDa for RBP1 and 195 kDa for RBP2) nuclear phosphoproteins with structural motifs that suggest a role in transcri ptional regulation. In addition we have been able to identify complexe s of pRB and RBP1 in vivo that are dissociated in the presence of puri fied human papillomavirus E7 protein.