Positive and Negative TAF sub(II) Functions That Suggest a Dynamic TFIID Structure and Elicit Synergy with TRAPs in Activator-Induced Transcription

• Published in: Molecular and cellular biology Vol. 21; no. 20; pp. 6882 - 6894
• Main Authors: Guermah, M, Tao, Y, Roeder, R G
• Format: Journal Article
• Language: English
• Published: 01.10.2001
• Subjects: histone H2A; histone H2B; TAFII135 protein; TAFII150 protein; TAFII20 protein; TFIID protein
• ISSN: 0270-7306
• DOI: 10.1128/MCB.21.20.6882-6894.2001

Human transcription factor TFIID contains the TATA-binding protein (TBP) and several TBP-associated factors (TAF sub(II)s). To elucidate the structural organization and function of TFIID, we expressed and characterized the product of a cloned cDNA encoding human TAF sub(II)135 (hTAF sub(II)135). Comparative far Western blots have shown that hTAF sub(II)135 interacts strongly with hTAF sub(II)20, moderately with hTAF sub(II)150, and weakly with hTAF sub(II)43 and hTAF sub(II)250. Consistent with these observations and with sequence relationships of hTAF sub(II)20 and hTAF sub(II)135 to histones H2B and H2A, respectively, TFIID preparations that contain higher levels of hTAF sub(II)135 also contain higher levels of hTAF sub(II)20, and the interaction between hTAF sub(II)20 and hTAF sub(II)135 is critical for human TFIID assembly in vitro. From a functional standpoint, hTAF sub(II)135 has been found to interact strongly and directly with hTFIIA and (within a complex that also contains hTBP and hTAF sub(II)250) to specifically cooperate with TFIIA to relieve TAF sub(II)250-mediated repression of TBP binding and function on core promoters. Finally, we report a functional synergism between TAF sub(II)s and the TRAP/Mediator complex in activated transcription, manifested as hTAF sub(II)-mediated inhibition of basal transcription and a consequent TRAP requirement for both a high absolute level of activated transcription and a high and more physiological activated/basal transcription ratio. These results suggest a dynamic TFIID structure in which the switch from a basal hTAF sub(II)-enhanced repression state to an activator-mediated activated state on a promoter may be mediated in part through activator or coactivator interactions with hTAF sub(II)135.