MULTIPLE TAF(II)S DIRECTING SYNERGISTIC ACTIVATION OF TRANSCRIPTION

Coordinate activation of transcription by multiple enhancer binding factors is essential for the regulation of pattern formation during development of Drosophila melanogaster. Cell-free transcription reactions are described that recapitulate transcriptional synergism directed by the Drosophila developmental regulators Bicoid (BCD) and Hunchback (HB). Within the basal transcription factor complex TFIID, two specific targets, TAF(II)110 and TAF(II)60, served as coactivators to mediate transcriptional activation by these two enhancer binding proteins. A quadruple complex containing TATA binding protein (TBP), TAF(II)250, TAF(II)110, and TAF(II)60 mediated transcriptional synergism by BCD and HB, whereas triple TBP-TAF(II) complexes lacking one or the other target coactivator failed to support synergistic activation. Deoxyribonuclease I footprint protection experiments revealed that an integral step leading to transcriptional synergism involves the recruitment of TBP-TAF(II) complexes to the promoter by way of multivalent contacts between activators and selected TAF(II)s. Thus, the concerted action of multiple regulators with different coactivators helps to establish the pattern and level of segmentation gene transcription during Drosophila development.