Specific requirement of mediator components in gene activation of drosophila melanogastex

Abstract

A Mediator complex is the major, multi-protein transcriptional coactivator complex in Saccaharomyces cerevisiae and Higher eukaryotes. A Mediator of Higher Eukaryotes like Drosophila and human is consisted of a subset of proteins conserved within metazoans and the other subset of proteins that are conserved throughout development. To decipher the mechanistic roles of Mediator proteins in regulating developmental specific gene expression, we isolated and analyzed a multiprotein complex containing Drosophila Mediator (dMediator) homologs. dMediator complex interacted with diverse sets of transcriptional activator proteins to elicit sophisticated regulation of gene expression and was critical for activated transcription in response to diverse transcriptional activators. The distinct phenotypes associated with certain mutations in some of the Mediator genes and the specific in vitro interactions of Mediator gene products with transcriptional activator proteins suggest the presence of activator-specific binding subunits within the Mediator complex. However, the physiological relevance of these selective in vitro interactions has not been addressed. Therefore, we analyzed dTRAP80, one of the putative activator binding subunit of Mediator, for specificity of binding to a number of natural transcriptional activators from Drosophila. Among the group of tested activator proteins (Armadillo, Dif, Hsf, Notch, RxR, VP16) that requires Mediator complex for transcriptional activation, only a subset (Dif, Hsf, Notch, RxR, VP16) of these proteins interacted with dTRAP80 in vitro, and only these dTRAP80-interacting activators were defective for activation under dTRAP80-deficient in vivo conditions. In particular, activation of Drosophila antimicrobial peptide (AMP) drosomycin gene expression by NF-κB-like transcription factor Dif during induction of the Toll signaling pathway was dependent on dTRAP80 module. These results, and the indirect support from the dTRAP80 artificial rec...