The p250 subunit of native TATA box-binding factor TFIID is the cell-cycle regulatory protein CCG1.

The protein TFIID is a general transcription factor which initiates preinitiation complex assembly through direct interaction with the TATA promoter element. It is a multisubunit complex containing a small TATA-binding polypeptide (TBP) and other TBP-associated factors (TAFs) ranging in size from about 30-250K (refs 7-10). Although native TFIID can mediate both activator-independent (basal) and activator-dependent transcription in reconstituted systems, TBP itself can mediate only basal transcription, even in cases where TBP or the general factor TFIIB are known to interact directly with transcriptional activators. TFIID subunits other than TBP must therefore be essential cofactors, and thus potential targets for activators, consistent with earlier demonstrations that activators interact with TFIID (refs 3, 5, 16, 17). Here we show that the 250K subunit of TFIID is identical to a gene product previously implicated in progression through the late G1 phase of the cell cycle. Part of p250 may thus serve a specific function in the activation of a subset of genes important for cell cycle progression.