RETRACTED: TAFIIs Mediate Activation of Transcription in the Drosophila Embryo

Frank Sauer,† David A. Wassarman,*† 1995b). Bicoid is part of a cascade of transcription factors that controls the formation of a segmented body Gerald M. Rubin, and Robert Tjian Howard Hughes Medical Institute plan in the early Drosophila embryo (Jäckle and Sauer, 1993). The bicoid gene (bcd) encodes a homeodomain Department of Molecular and Cell Biology University of California protein that forms an anterior/posterior concentration gradient in the embryo (Driever and Nüsslein-Volhard, Berkeley, California 94720-3204 1988a). Genetic and molecular analyses suggest that Bicoid initiates the formation of anterior body structures by selectively activating the transcription of several zySummary gotic segmentation genes (Hoch and Jäckle, 1993). Bicoid acts synergistically with another factor, HunchMutations in the genes for two highly conserved TAFs, back. We described previously an in vitro reconstituted TAFII60 and TAFII110, reduce transcription of Bicoidtranscription system responsive to Bicoid and Hunchdependent target genes in vivo. By means of several back that allowed us to formulate a molecular mechadistinct genetic test systems, specific activator–TAF nism for the transcriptional synergy that is found beinteractions are shown to support both simple and tween these factors. (Sauer et al., 1995a; 1995b). Direct synergistic enhancement of transcription in the emprotein-binding assays revealed that the glutamine-rich bryo. These studies provide in vivo evidence that TAFs activation domain of Bicoid contacts TAFII110, one of can serve as coactivators to receive gene-specific the subunits of TFIID. By contrast, the alanine-rich actitranscriptional activation signals. This genetic system vation domain of Bicoid, as well as the Hunchback actialso presents the opportunity to study the function of vation domain, was found to interact with TAFII60, basal transcription components in regulating developanother subunit of TFIID. Multiple and presumably siment of complex organisms. multaneous activation domain–TAF interactions contribute to synergistic activation of transcription in vitro by Introduction enhancing or stabilizing the binding of TFIID to the promoter. These biochemical studies reveal a possible role Metazoan organisms undergo complex developmental for TAFs in mediating both simple and synergistic tranprograms that are orchestrated by precise temporal and scriptional activation of Drosophila genes. However, it spatial patterns of transcription (St. Johnston and Nüssremained unknown whether TAFs are also required for lein-Volhard, 1992; Hoch and Jäckle, 1993; De Robertis transcription in vivo and whether they operate by these and Sasai, 1996). In vitro studies suggest that activation same mechanisms in Drosophila. of transcription is governed by the assembly of multiproTo establish a sensitized genetic system in which to tein complexes at the core promoter of eukaryotic genes screen for potential Drosophila TAF mutants, we have (Tjian and Maniatis, 1994; Roeder, 1996). This process taken advantage of the unique properties offered by is modulated and enhanced by specialized transcription transcription and signal transduction pathways that opfactors that bind directly to target genes via sequenceerate during Drosophila eye development (Wassarman specific DNA-binding domains. Once tethered to speet al., 1995). Here, we report the isolation of mutant cific control elements of a gene, appropriately exposed alleles for TAFII60 and TAFII110 in a genetic screen sensiactivation domains of enhancer-binding proteins are tive to transcription levels. Characterization of the TAF thought to contact various components of the general proteins encoded by the mutant alleles reveal that they transcriptional machinery that include basal factors fail to become incorporated into TFIID in vivo. Since (TFIIA, TFIIB, TFIID, TFIIE, TFIIF, and TFIIH), RNA polyTAFII60 and TAFII110 were found to be targets of Bicoid merase II, and associated multiprotein cofactors (Verbased on previous in vitro experiments, it became feasirijzer and Tjian, 1996; Roeder, 1996). ble to directly test the functional relevance of Bicoid– Many eukaryotic activators have been found to interTAF interactions in mediating activation of transcription act with one or more subunits of the essential transcripin the Drosophila embryo. We present evidence that tion factor, TFIID, comprised of the TATA-binding proboth TAFII60 and TAFII110 are required for Bicoid-depentein (TBP) and some eight different TBP-associated dent activation of segmentation gene transcription in factors (TAFs) (Verrijzer and Tjian, 1996). Different activivo. Our results also suggest that TAFs serve as coactivators are able to contact distinct TAFs within the TFIID vators responsible for both simple and synergistic trancomplex to mediate activation of transcription in vitro scription during development of the Drosophila embryo. (Chen etal., 1994). We previously identified the Drosophila transcription factor, Bicoid, as an activator that utilizes TAFs to mediate transcriptional activation in reconResults stituted transcription reactions (Sauer et al., 1995a;