Suzuki et al., 1988), and some were shown to interact to establish a unified MED nomenclature in order to directly with Pol II and GTFs (Koleske et al., 1992; Myers enhance understanding of the scientific literature by a et al., 1998; Sakurai and Fukasawa, 2000; Thompson et wide audience and to aid cross-species comparisons al., 1993). Further genetic studies demonstrated the role and proper annotation of sequence databases. of Mediator in repression as well as activation (Li et al., The unified nomenclature, shown in Table 1, is based 1995; Song et al., 1996), and established the relevance on the following considerations: of Mediator to transcription control in vivo (Barberis et al., 1995; Holstege et al., 1998; Thompson and Young, 1995). 1. The new nomenclature complies with guidelines endorsed by the Saccharomyces Genome Database For some time there was no evidence for conservation of yeast Mediator through evolution. However, indepen-(SGD), the FlyBase and WormBase resources, and the human HUGO Gene Nomenclature Committees. dent biochemical and structural studies of coactivators that, in most cases, were initially identified in functional 2. MED is the most explicit acronym. 3. This nomenclature acknowledges the discovery of assays have revealed true counterparts in other fungi and in higher organisms (Asturias et al., 1999; Boyer et MED complexes in yeast. 4. In light of point 3, the original yeast MEDs will retain al., 1999; Chao et al., 1996; Fondell et al., 1996; Gu et al., 1999, 2002; Ito et al., 1999; Jiang et al., 1998; theirnames (MED1-11; notethattheMED5acronym will replace Nut1). Kretzschmar et al., 1994; Kwon et al., 1999; Malik et al., 2000; Meisterernst et al., 1991; Naar et al., 1999; Park 5. The remaining yeast MEDs will be given names starting from MED12, in order of decreasing conet al., 2001; Rachez et al., 1999; Ryu et al., 1999; Spahr et al., 2001; Sun et al., 1998). In mammals, the positive ceptual molecular weights deduced from primary sequences. cofactor (PC2) component of the USA coactivator activity (Kretzschmar et al., 1994; Meisterernst et al., 1991) 6. MEDs found outside budding yeast will be given names starting from MED23 in order of decreasing proved to be a Mediator-related complex (Malik et al., 2000). Similarly, the human TRAP complex, first identi- calculated molecular weights (based on the human protein). At present, this list extends to MED31. fied as a discrete group of thyroid hormone receptorassociated polypeptides with a potent coactivator activ- 7. Future bona fide new MED components will be assigned numbers starting from MED32. ity (Fondell et al., 1996), also was found to represent a Mediator equivalent (Ito et al., 1999). Other metazoan 8. The general nomenclature will employ CDK8 and CycC, as the CDK-cyclin couple is readily identifi-Mediator-related complexes have been denoted ARC, CRSP, or DRIP owing to interactions with other nuclear able for a wide scientific audience. 9. Except for the specific case of C. elegans (see point receptors as well as diverse transcriptional activators (Mittler et al., 2003; Naar et al., 1999; Rachez et al., 1999; 10), paralogs in the same organism will be termed MED-like, eg, MED12L in humans. Ryu et al., 1999; Yang et al., 2004). A systematic analysis of proteins present in the most 10. C. elegans MEDs will retain the specific nomenclature already adopted by WormBase, the MED acrohighly purified mammalian complexes by tandem mass spectrometry led to the identification of up to 30 distinct nym being used for another gene category. Thus