Mediator Expression Profiling Epistasis Reveals a Signal Transduction Pathway with Antagonistic Submodules and Highly Specific Downstream Targets

• Published in: Molecular cell 2005-08, Vol.19 (4), p.511-522
• Main Authors: van de Peppel, Jeroen, Kettelarij, Nienke, van Bakel, Harm, Kockelkorn, Thessa T.J.P., van Leenen, Dik, Holstege, Frank C.P.
• Format: Article
• Language: English
• Subjects: Chromosomal Proteins, Non-Histone - genetics; Chromosomal Proteins, Non-Histone - metabolism; Cyclin-Dependent Kinase 8; Cyclin-Dependent Kinases - genetics; Cyclin-Dependent Kinases - metabolism; Down-Regulation; Epistasis, Genetic; Gene Deletion; Gene Expression Profiling; Gene Expression Regulation, Fungal; Mediator Complex; Phosphorylation; RNA Polymerase II - metabolism; Saccharomyces cerevisiae - genetics; Saccharomyces cerevisiae - metabolism; Saccharomyces cerevisiae Proteins - genetics; Saccharomyces cerevisiae Proteins - metabolism; Signal Transduction - genetics; Trans-Activators - genetics; Trans-Activators - metabolism; Transcription Factors - genetics; Transcription Factors - metabolism; Up-Regulation
• ISSN: 1097-2765; 1097-4164
• DOI: 10.1016/j.molcel.2005.06.033

Mediator is an evolutionarily conserved coregulator of RNA polymerase II transcription. Microarray structure-function analysis of S. cerevisiae Mediator reveals functional antagonism between the cyclin-dependent kinase (Cdk) submodule and components from the Tail (Med15, Med2, Med3), Head (Med20, Med18), and Middle (Med31). Certain genes exhibit increased or decreased expression, depending on which subunit is deleted. Epistasis analysis with expression-profile phenotypes shows that MED2 and MED18 are downstream of CDK8. Strikingly, Cdk8-mediated modification of a single amino acid within Mediator represses the regulon of a single transcription factor, Rcs1/Aft1. Highly specific gene regulation is thought to be determined by activators and combinatorial use of cofactors. Here, subtle modification of the general transcription machinery through one of its own components is shown to determine highly specific expression patterns. Expression profiling can therefore precisely map regulatory cascades, and our findings support a role for Mediator as a direct processor of signaling pathways for determining specificity.