MULTIPLE TAF(II)S DIRECTING SYNERGISTIC ACTIVATION OF TRANSCRIPTION

Coordinate activation of transcription by multiple enhancer binding fa ctors is essential for the regulation of pattern formation during deve lopment 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 t argets, TAF(II)110 and TAF(II)60, served as coactivators to mediate tr anscriptional activation by these two enhancer binding proteins. A qua druple 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. Deoxyribonuclea se I footprint protection experiments revealed that an integral step l eading to transcriptional synergism involves the recruitment of TBP-TA F(II) complexes to the promoter by way of multivalent contacts between activators and selected TAF(II)s. Thus, the concerted action of multi ple regulators with different coactivators helps to establish the patt ern and level of segmentation gene transcription during Drosophila dev elopment.