Med19(Rox3) Regulates Intermodule Interactions in the Saccharomyces cerevisiae Mediator Complex

Abstract

The Saccharomyces cerevisiae Mediator is a 25-subunit complex that facilitates both transcriptional activation and repression. Structural and functional studies have divided Mediator subunits into four distinct modules. The Head, Middle, and Tail modules form the core functional Mediator complex, whereas a fourth, the Cyc-C module, is variably associated with the core. By purifying Mediator from a strain lacking the Med19(Rox3) subunit, we have found that a complex missing only the Med19(Rox3) subunit can be isolated under mild conditions. Additionally, we have established that the entire Middle module is released when the ⌬med19(rox3) Mediator is purified under more stringent conditions. In contrast to most models of the modular structure of Mediator, we show that release of the Middle module in the ⌬med19(rox3) Mediator leaves a stable complex made up solely of Head and Tail subunits. Both the intact and Head-Tail ⌬med19(rox3) Mediator complexes have defects in enhanced basal transcription, enhanced TFIIH phosphorylation of the CTD, as well as binding of RNA Pol II and the CTD. The largely intact ⌬med19(rox3) complex facilitates activated transcription at levels similar to the wild type Mediator. In the absence of the Middle module, however, the ⌬med19(rox3) Mediator is unable to facilitate activated transcription. Although the Middle module is unnecessary for holding the Head and Tail modules together, it is required for the complex to function as a conduit between activators and the core transcription machinery.

Role of Mediator in Regulating Pol II Elongation and Nucleosome Displacement in Saccharomyces cerevisiae

“…Also consistent is the similar phenotype of med19-1002, given that Med19 has been implicated in stabilizing the association of the middle module with the rest of Mediator (Baidoobonso et al 2007). A caveat to the above is that our data do not formally rule out the possibility that the Mediator mutations affect mRNA stability instead of, or in addition to, transcription.…”

“…The middle module confers structural integrity to Mediator (Baumli et al 2005). It also facilitates activated transcription in purified systems (Baidoobonso et al 2007) and has a dual role in both activation and repression in cells (Tabtiang and Herskowitz 1998;Gromoller and Lehming 2000;Singh et al 2006). The middle module also has been implicated in regulating transcriptional silencing (Zhu et al 2011a) and interaction with histone tails (Zhu et al 2011b).…”

The Mediator Complex in Plants: Structure, Phylogeny, and Expression Profiling of Representative Genes in a Dicot (Arabidopsis) and a Monocot (Rice) during Reproduction and Abiotic Stress

“…In addition, a fourth regulatory module comprising two Med subunits along with a cyclin-dependent kinase, Cdk8, and its associated cyclin, CycC, collectively called the kinase or Cdk8-cyclin C module, is also part of the Med complex. In contrast to the above model, Baidoobonso et al (2007) reported an intact and stable complex comprising only the tail and head modules without the middle module. Until recently, the metazoan Med complexes were known to share 22 Med subunits with S. cerevisiae , having eight subunits (Med23 to -30) unique to them.…”

The role of Med19 in the proliferation and tumorigenesis of human hepatocellular carcinoma cells

“…In addition to stimulating basal transcription, the Mediator complex plays a crucial role in the activation and repression of eukaryotic mRNA synthesis [11,12] . The Mediator complex, which consists of at least 20 subunits with multiple activities, including Rox3 (Med19), was first characterized through biochemical and genetic studies in Saccharomyces cerevisiae in the early 1990s [13,14] .…”