Retinoblastoma binding protein, also known as RBBP9, localizes to both the nucleus and the cytoplasm. RBBP9 is a retinoblastoma binding protein that may play a role in the regulation of cell proliferation and differentiation. Specifically, RBBP9 interacts with retinoblastoma(Rb) and provides cellular resistance to the growthinhibitory effects of TGFbeta1, thus facilitating the cellular transformation process.