Molecular cloning of a novel 120-kDa TBP-interacting protein.

TATA-binding protein (TBP) is a central component for transcriptional regulation and is a target for various transcription regulators. Using histidine-tagged TBP as a ligand for affinity-purification of proteins bound to TBP, we purified a 120-kD protein, termed TBP-interacting protein 120 (TIP120), from rat liver nuclear extracts. The entire cDNA sequence of TIP120 contained an open reading frame encoding a novel polypeptide of 1230 amino acids. The recombinant TIP120 interacted directly with TBP under a physiological condition in vitro. Immunoprecipitation analysis indicated that TIP120 was associated with TBP in nuclear extracts. Interestingly, the N-terminal region of TIP120 exhibited sequence similarity to that of Drosophila TAF80, which was shown to bind directly to TBP. This novel TBP-binding protein is considered to participate in transcription regulation through the interaction with TBP.