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Gene Review

SRB4  -  Srb4p

Saccharomyces cerevisiae S288c

Synonyms: MED17, Mediator complex subunit 17, Mediator of RNA polymerase II transcription subunit 17, Suppressor of RNA polymerase B 4, YER022W
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High impact information on SRB4

  • We also show that transcription of these Kin28-independent genes is independent of Srb4 and Srb6, critical components of the CTD-associated transcriptional mediator complex [1].
  • These data, and the analysis of an rgr1 mutant, point to an Rgr1 subcomplex of the SRB/mediator as the mechanistic route of activation by Srb4-independent activators in vivo [2].
  • Here, we show that transcriptional activation by different natural activators, and by artificial recruitment of various transcription factors, have very different degrees of Srb4 independence [2].
  • The upstream-activating sequence (UAS) of the CUP1 promoter was sufficient to drive Cu2+ inducible transcription without Srb4 and heat shock inducible transcription without the CTD [3].
  • We demonstrate here, through affinity chromatography, photo-cross-linking, and surface plasmon resonance experiments, that the GAL4 activator interacts directly with the SRB4 subunit of the RNA polymerase II holoenzyme [4].

Biological context of SRB4

  • A single missense mutation in SRB4 can specifically suppress transcriptional defects caused by the med6 ts mutation, indicating a functional interaction between these two mediator subunits in the activation of transcription [5].
  • These results suggest that distinct Mediator proteins in the Rgr1 subcomplex are required for activator-specific transcriptional activation and that the activation signals mediated by these Mediator proteins converge on Med6 (or the Srb4 subcomplex) to modulate Pol II activity [6].
  • Since the Srb4 subunit of the holoenzyme is essential for expression of most class II genes and is a target of at least one transcriptional activator, we reasoned that suppressors of a temperature-sensitive mutation in Srb4 would identify other factors generally involved in regulation of gene expression [7].
  • Purified recombinant Srb4 subcomplex stimulated basal transcription of pol II but had little effect on activated transcription and phosphorylation of the C-terminal domain of the Rpb1 subunit of pol II [8].
  • The Med17 subunit is located within the head domain and is essential for cell viability [9].

Associations of SRB4 with chemical compounds

  • The Mediator complex is composed of two subcomplexes, the Rgr1 and Srb4 subcomplexes, which appear to function in the reception of activator signals and the subsequent modulation of Pol II activity, respectively [6].

Other interactions of SRB4

  • The physiological relevance of this interaction is confirmed by mutations in SRB4, which occur within its GAL4-binding domain and which restore activation in vivo by a GAL4 derivative bearing a mutant activation domain [4].


  1. Transcriptional activation independent of TFIIH kinase and the RNA polymerase II mediator in vivo. Lee, D., Lis, J.T. Nature (1998) [Pubmed]
  2. Different upstream transcriptional activators have distinct coactivator requirements. Lee, D.K., Kim, S., Lis, J.T. Genes Dev. (1999) [Pubmed]
  3. Activated transcription independent of the RNA polymerase II holoenzyme in budding yeast. McNeil, J.B., Agah, H., Bentley, D. Genes Dev. (1998) [Pubmed]
  4. An activator target in the RNA polymerase II holoenzyme. Koh, S.S., Ansari, A.Z., Ptashne, M., Young, R.A. Mol. Cell (1998) [Pubmed]
  5. Requirement for a functional interaction between mediator components Med6 and Srb4 in RNA polymerase II transcription. Lee, Y.C., Kim, Y.J. Mol. Cell. Biol. (1998) [Pubmed]
  6. Activator-specific requirement of yeast mediator proteins for RNA polymerase II transcriptional activation. Han, S.J., Lee, Y.C., Gim, B.S., Ryu, G.H., Park, S.J., Lane, W.S., Kim, Y.J. Mol. Cell. Biol. (1999) [Pubmed]
  7. Interplay of positive and negative regulators in transcription initiation by RNA polymerase II holoenzyme. Lee, T.I., Wyrick, J.J., Koh, S.S., Jennings, E.G., Gadbois, E.L., Young, R.A. Mol. Cell. Biol. (1998) [Pubmed]
  8. The structural and functional organization of the yeast mediator complex. Kang, J.S., Kim, S.H., Hwang, M.S., Han, S.J., Lee, Y.C., Kim, Y.J. J. Biol. Chem. (2001) [Pubmed]
  9. The classical srb4-138 mutant allele causes dissociation of yeast Mediator. Linder, T., Zhu, X., Baraznenok, V., Gustafsson, C.M. Biochem. Biophys. Res. Commun. (2006) [Pubmed]
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