Mediator exists in a free form containing the Med12, Med13, CDK8, and CycC subunits (the Srb8-11 module) and a smaller form, which lacks these four subunits and associates with RNA polymerase II (Pol II), forming a holoenzyme. We use chromatin immunoprecipitation (ChIP) and DNA microarrays to investigate genome-wide localization of Mediator and the Srb8-11 module in fission yeast. Mediator and the Srb8-11 module display similar binding patterns, and interactions with promoters and upstream activating sequences correlate with increased transcription activity. Unexpectedly, Mediator also interacts with the downstream coding region of many genes. These interactions display a negative bias for positions closer to the 5' ends of open reading frames (ORFs) and appear functionally important, because downregulation of transcription in a temperature-sensitive med17 mutant strain correlates with increased Mediator occupancy in the coding region. We propose that Mediator coordinates transcription initiation with transcriptional events in the coding region of eukaryotic genes.

The human mitochondrial transcription termination factor (mTERF) is involved in the regulation of transcription of the mitochondrial genome. Similarity searches and phylogenetic analysis demonstrate that mTERF is a member of large and complex protein family (the MTERF family) shared amongst metazoans and plants. Interestingly, we identify three novel MTERF genes in vertebrates, which all encode proteins with predicted mitochondrial localization. Members of the MTERF family have so far not been detected in fungi, supporting the notion that mitochondrial transcription regulation may have evolved separately in yeast and animal cells.

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Mediator is an evolutionary conserved coregulator complex required for transcription of almost all RNA polymerase II-dependent genes. The Schizosaccharomyces pombe Mediator consists of two dissociable components—a core complex organized into a head and middle domain as well as the Cdk8 regulatory subcomplex. In this work we describe a functional characterization of the S. pombe Mediator. We report the identification of the S. pombe Med20 head subunit and the isolation of ts alleles of the core head subunit encoding med17+. Biochemical analysis of med8ts, med17ts, Δmed18, Δmed20 and Δmed27 alleles revealed a stepwise head domain molecular architecture. Phenotypical analysis of Cdk8 and head module alleles including expression profiling classified the Mediator mutant alleles into one of two groups. Cdk8 module mutants flocculate due to overexpression of adhesive cell-surface proteins. Head domain-associated mutants display a hyphal growth phenotype due to defective expression of factors required for cell separation regulated by transcription factor Ace2. Comparison with Saccharomyces cerevisiae Mediator expression data reveals that these functionally distinct modules are conserved between S. pombe and S. cerevisiae.

Edible microbial biomass derived from bacteria, yeasts, filamentous fungi or microalgae is a promising alternative to conventional sources of food and feed. Microorganisms are a good source of protein, vitamins and, in some cases, also contain beneficial lipids. The ability of microorganisms to use simple organic substrates for growth permits industrial-scale cultivation of edible microbial biomass in geographical locations that would not compete with agricultural production. Only a handful of microbial products are currently available for human consumption. The use of microbial biomass for animal feed is limited by access to low-cost growth substrates and competition from conventional feed sources such as soy and fishmeal. At a time when the global food production system is threatened by the effects of climate change, the production of edible microorganisms has the potential to circumvent many of the current environmental boundaries of food production as well as reducing its environmental impact. Photosynthetic microorganisms such as cyanobacteria and microalgae can be cultivated for food and feed independently of arable land. In addition, recent technological developments in atmospheric carbon dioxide (CO 2) capture, extraction and catalytic conversion into simple organic compounds can be used for cultivation of edible microbial biomass for food and feed in a manner that is wholly independent of photosynthesis. The future possibilities, challenges and risks of scaled-up production of edible microbial biomass in relation to the global food system and the environment are discussed.