The mediator complex is required for the expression of nearly all RNA pol II dependent genes in Saccharomyces cerevisiae. Deletion of the MED5 gene leads to increased transcription of nuclear genes encoding components of the oxidative phosphorylation machinery, and decreased transcription of mitochondrial genes encoding components of the same machinery [1]. There is no orthologue from pombe, and this subunit appears to be fungal specific [2].

1: The structural and functional role of Med5 in the yeast Mediator tail module. Beve J, Hu GZ, Myers LC, Balciunas D, Werngren O, Hultenby K, Wibom R, Ronne H, Gustafsson CM; J Biol Chem. 2005;280:41366-41372. PMID:16230344

2: A unified nomenclature for protein subunits of mediator complexes linking transcriptional regulators to RNA polymerase II. Bourbon HM, Aguilera A, Ansari AZ, Asturias FJ, Berk AJ, Bjorklund S, Blackwell TK, Borggrefe T, Carey M, Carlson M, Conaway JW, Conaway RC, Emmons SW, Fondell JD, Freedman LP, Fukasawa T, Gustafsson CM, Han M, He X, Herman PK, Hinnebusch AG, Holmberg S, Mol Cell. 2004;14:553-557. PMID:15175151