Project description:The multiprotein Mediator complex is an important regulator of RNA polymerase II-dependent genes in eukaryotic cell. In contrast to the situation in many other eukaryotes, the conserved Med15 protein is not a stable component of Mediator isolated from fission yeast. We now demonstrate that Med15 exists in a protein complex together with Hrp1, an ATP-dependent chromatin remodeling protein. The Med15/Hrp1 subcomplex is not a component of the core Mediator complex, but can interact with the repressive L-Mediator conformation. Deletion of MED15 and HRP1 cause similar effects on global steady-state levels of mRNA, but only MED15 is required for galactose-dependent activation of the inv1 gene. Hrp1 has been found in complex with other proteins and genome-wide analysis demonstrates that Med15 only associates with a distinct subset of Hrp1-bound gene promoters. Global analysis reveals that Hrp1-binding normally is associated with increased histone H3 density, but at promoters also bound by Med15, histone H3 density is instead increased. Our findings reveal that Med15 functions as a separate entity in fission yeast and indicate that the function and organization of the Mediator complex may differ significantly between eukaryotes. Keywords: ChIP-chip
Project description:Mediator is a co-regulator of RNA polymerase II (Pol II), transducing signals from regulatory elements and transcription factors to the general transcription machinery at the promoter. We here demonstrate that Med20 influences ribosomal protein expression in fission yeast. In addition, loss of Med20 leads to an accumulation of aberrant readthrough tRNA transcripts. The aberrant transcripts are polyadenylated and targeted for degradation by the exosome. Similarly, other specialized RNA molecules, such as snRNA, snoRNA and rRNA are also accumulated in the absence of Med20. We suggest that fission yeast Mediator takes part in a regulatory pathway of Pol III transcripts.
