Identification of Med26 target genes in Human HEK 293T cells

Med26 is a subunit of the Human Mediator complex. The Mediator complex is an evolutionarily conserved coregulatory complex that interacts with RNA polymerase II to regulate gene expression. In metazoa, Mediator is composed of some 30 distinct subunits. Mediator exists in multiple, functionally distinct forms that share a common core of subunits and can be distinguished by the presence or absence of a kinase module composed of Med12, Med13, Cdk8, and Cyclin C. In higher eukaryotes, a subset of Mediator complexes is associated with an additional subunit, Med26. This Med26-containing Mediator copurifies from cells with little or no kinase module, but near-stoichiometric Pol II. Evidence suggests that Med26-containing Mediator plays a key role in transcriptional activation however, the mechanism(s) by which Med26 contributes to this process are not known. To identify Med26 target genes, we used Affymetrix U133A plus 2.0 expression arrays to analyze mRNA expression in 293T cells from which Med26 had been depleted by transient transfection by each of three different siRNAs. Three different independent Med26 siRNA knockdowns were compared to a non-targeting control in triplicate, for a total of 12 samples.