This family of Med9 proteins is conserved in yeasts. It forms part of the middle region of Mediator [4]. Med9 has two functional domains. The species-specific amino-terminal half (aa 1-63) plays a regulatory role in transcriptional regulation, whereas this well-conserved carboxy-terminal half (aa 64-149) has a more fundamental function involved in direct binding to the amino-terminal portions of Med4 and Med7 and the assembly of Med9 into the Middle module. Also, some unidentified factor(s) in med9 extracts may impact the binding of TFIID to the promoter [5].

1: Identification of mammalian Mediator subunits with similarities to yeast Mediator subunits Srb5, Srb6, Med11, and Rox3. Sato S, Tomomori-Sato C, Banks CA, Sorokina I, Parmely TJ, Kong SE, Jin J, Cai Y, Lane WS, Brower CS, Conaway RC, Conaway JW; J Biol Chem 2003;278:15123-15127. PMID:12584197

2: A mammalian homolog of Drosophila melanogaster transcriptional coactivator intersex is a subunit of the mammalian Mediator complex. Sato S, Tomomori-Sato C, Banks CA, Parmely TJ, Sorokina I, Brower CS, Conaway RC, Conaway JW; J Biol Chem 2003;278:49671-49674. PMID:14576168

3: CSE1 and CSE2, two new genes required for accurate mitotic chromosome segregation in Saccharomyces cerevisiae. Xiao Z, McGrew JT, Schroeder AJ, Fitzgerald-Hayes M; Mol Cell Biol 1993;13:4691-4702. PMID:8336709

4: 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

5: Saccharomyces cerevisiae Med9 comprises two functionally distinct domains that play different roles in transcriptional regulation. Takahashi H, Kasahara K, Kokubo T; Genes Cells. 2009;14:53-67. PMID:19077037