Genetic dissection of hTAF(II)130 defines a hydrophobic surface required for interaction with glutamine-rich activators

The general transcription factor TFIID is a multiprotein complex consisting of the TATA box-binding protein and multiple TATA box-binding protein-asso ciated factors (TAF(II)s). The central domain of human TAF(II)130 contains four glutamine-rich regions Q1-Q4 that interact with transcriptional activa tors such as Sp1 and CREB and mediate activation. We screened in yeast rand om point mutations introduced into Q1-Q4 against the Sp1 activation domain and obtained a distinct set of hTAF(II)130s with alterations in TAF(II)-act ivator interaction. Here we characterize functionally an hTAF(II)130 mutant containing a phenylalanine to serine change at position 311 (F311S) that i s compromised in its ability to associate with Sp1B and CREB-N activation d omains. Substitution of phenylalanine with tyrosine but not with isoleucine or tryptophan also reduced hTAF(II)130 interaction, suggesting that the hy drophobic character rather than the specific amino acid at this position is a key determinant of interaction. Deletion of nine amino acids (Delta 9) s urrounding Phe(311) abolished the interaction of hTAF(II)130 with Sp1. Over expression of hTAF(II)130Q1/Q2 and Q1-Q4 strongly inhibited Sp1-dependent t ranscriptional enhancement in transient transfection assays, whereas expres sion of either F311S or Delta 9 only partially suppressed Sp1-mediated acti vation. Thus, a short hydro phobic sequence motif encompassing Phe(311) in hTAF(II)130 represents a critical surface with which Sp1B interacts to acti vate transcription.