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Saccharomyces cerevisiae Med9 comprises two functionally distinct domains that play different roles in transcriptional regulation.

Division of Molecular and Cellular Biology, International Graduate School of Arts and Sciences, Yokohama City University, Yokohama 230-0045, Japan.
Genes to Cells (Impact Factor: 2.73). 01/2009; 14(1):53-67. DOI: 10.1111/j.1365-2443.2008.01250.x
Source: PubMed

ABSTRACT Mediator is one of the most important co-activators that function in eukaryotic transcriptional regulation. In Saccharomyces cerevisiae, Mediator is comprised of 25 subunits belonging to four structurally distinct modules: Head, Middle, Tail, and Cyc-C. Although each module plays a critical role in the regulation of a distinct set of genes, the precise molecular mechanisms remain unclear. To gain new insight into the role of the less-characterized Middle module, we analyzed the function of Med9 by constructing a set of mutants and subjecting them to a range of in vivo and in vitro assays. Our results demonstrate that Med9 has two functional domains. The species-specific amino-terminal half (aa 1-63) plays a regulatory role in transcriptional regulation in vivo and in vitro. In contrast, the well-conserved carboxy-terminal half (aa 64-149) has a more fundamental function involved in direct binding to the amino-terminal portions of Med4 and Med7 and the assembly of Med9 into the Middle module. Importantly, activator-dependent recruitment of TBP and Taf11 to the promoter is differentially affected in med9 extracts and in extracts lacking Mediator. Add-back experiments indicate that some unidentified factor(s) in med9 extracts may impact the binding of TFIID to the promoter.

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