DROSOPHILA 230-KD TFIID SUBUNIT, A FUNCTIONAL HOMOLOG OF THE HUMAN CELL-CYCLE GENE-PRODUCT, NEGATIVELY REGULATES DNA-BINDING OF THE TATA BOX-BINDING SUBUNIT OF TFIID

A Drosophila cDNA encoding the largest TFIID subunit (p230) was isolated using a degenerate oligodeoxynucleotide probe based on an amino acid sequence of the purified protein. The entire cDNA sequence contains an open reading frame encoding a polypeptide of 2068 amino acids, corresponding to a calculated molecular mass of 232 kD. The deduced amino acid sequence showed a strong sequence similarity with the protein encoded by a human gene (CCG1) implicated in cell cycle progression through G1, suggesting that p230 may be a target for cell cycle regulatory factors. The recombinant protein expressed in Sf9 cells via a baculovirus vector interacts directly with the TATA box-binding subunit of TFIID (TFIIDtau or TBP) from Drosophila, human, and yeast. Surprisingly, recombinant p230 inhibits the TATA box-binding activity and function of TFIIDtau, suggesting that p230 interactions with TFIIDtau, and possible modulations thereof by other factors may play an important role in TFIID function.