We have discovered a nuclear protein in normal human cells, 'retinoblastoma-associated protein 1' ('RBAP-1') that binds directly to the retinoblastoma protein pocket of the underphosphorylated form of the retinoblastoma protein ('RB') and does not bind to phosphorylated RB or to RB with inactivating mutations. The translated RBAP-1 sequence does not resemble other proteins whose sequences are known, and RBAP-1 does not contain a sequence homologous to the transforming element common to viral proteins that bind to the RB pocket. RBAP-1 and the E2F transcription activity have similar DNA-binding specificities and can bind to at least some of the same proteins, such as RB and E4.
RETINOBLASTOMA-ASSOCIATED PROTEIN 1 cDNA