MULTIPLE INTERACTIONS BETWEEN HTAF(II)55 AND OTHER TFIID SUBUNITS - REQUIREMENTS FOR THE FORMATION OF STABLE TERNARY COMPLEXES BETWEEN HTAF(II)55 AND THE TATA-BINDING PROTEIN

We have cloned and characterized the human TATA-binding protein (TBP)- associated factor hTAF(II)55. hTAF(II)55, which has no known Drosophil a counterpart, is present in both of the previously described TFIID al pha and TFIID beta subpopulations. We describe the interactions of hTA F(II)55 with other subunits of the transcription factor TFIID. By cotr ansfection in COS cells, we show that hTAF(II)55 interacts with hTAF(I I)250, hTAF(II)100, hTAF(II)28, hTAF(II)20, and hTAF(II)18, but not wi th hTAF(II)30 or TBP. Analysis of the binding of hTAF(II)55 and TBP to hTAF(II)28 deletion mutants indicates that distinct regions of hTAF(I I)28 are required for these interactions. Although hTAF(II)55 does not interact by itself with TBP, stable ternary complexes containing hTAF (II)55 and TBP can be formed in the presence of hTAF(II)250, hTAF(II)1 00, or hTAF(II)28. These results not only show that hTAF(II)100 and hT AF(II)28 interact with TBP, but also that they can nucleate the format ion of partial TFIID complexes.