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Gene Review

SSN8  -  Ssn8p

Saccharomyces cerevisiae S288c

Synonyms: CNC1, GIG3, N2805, NUT9, RNA polymerase II holoenzyme cyclin-like subunit, ...
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Disease relevance of SSN8


High impact information on SSN8

  • Genetic and biochemical evidence indicates that the SRB10 and SRB11 proteins form a kinase-cyclin pair in the holoenzyme [2].
  • Ume3p mutants resistant to degradation resulted in a 2-fold reduction in SPO13 mRNA levels during meiosis, indicating that the down-regulation of this cyclin is important for normal meiotic gene expression [3].
  • Here we report that UME3 is also required for the full repression of the HSP70 family member SSA1 [3].
  • However, Ume3p is destroyed during meiosis or when cultures are subjected to heat shock [3].
  • UME3 encodes a non-essential C-type cyclin (Ume3p) whose levels do not vary through the mitotic cell cycle [3].

Biological context of SSN8

  • This report demonstrates that Ume3p levels are also reduced in cultures subjected to ethanol shock, oxidative stress, or carbon starvation or during growth on nonfermentable carbons [4].
  • Second, Srb11p is required for the efficient execution of meiosis I. srb11delta mutants either exhibited a delay in performing meiosis I and meiosis II or skipped meiosis I entirely [5].
  • First, SRB11 is required for the normal exit from the mitotic cell cycle prior to meiotic induction [5].
  • Specifically, mutants lacking SRB11 (srb11delta) uncouple bud growth from chromosome segregation, producing small buds with nuclei [5].
  • Genetic interactions among srb mutations imply that a balance between the activities of Srb8 + Srb10 and Srb11 is important for normal cell growth [6].

Anatomical context of SSN8


Associations of SSN8 with chemical compounds


Physical interactions of SSN8

  • We used the split-ubiquitin system to demonstrate that Tup1p interacts with Srb11p in vivo [9].

Regulatory relationships of SSN8

  • Finally, a ume3 null allele suppresses the growth defect of plc1 mutants in response to either elevated temperature or the presence of hydrogen peroxide [4].
  • Genetic analysis indicates that the SSN3-SSN8 complex contributes to transcriptional repression of diversely regulated genes and also affects induction of the GAL1 promoter [10].

Other interactions of SSN8

  • Previous work showed that a cyclin-dependent kinase-cyclin pair encoded by SSN3 and SSN8, two members of the SSN suppressor family, are identical to two SRB proteins in the mediator [11].
  • Oxidative stress-induced destruction of the yeast C-type cyclin Ume3p requires phosphatidylinositol-specific phospholipase C and the 26S proteasome [4].
  • This model is supported by the finding that overexpression of the meiotic inducer IME2 partially restored the ability of srb11 mutants to perform meiosis I [5].
  • We propose that Tup1p targets the cyclin Srb11p to affect the cyclin-dependent kinase Srb10p [9].
  • Finally, Ume3p destruction was not affected in mutants defective for ubiquitin-dependent proteolysis [3].


  1. Ask10p mediates the oxidative stress-induced destruction of the Saccharomyces cerevisiae C-type cyclin Ume3p/Srb11p. Cohen, T.J., Lee, K., Rutkowski, L.H., Strich, R. Eukaryotic Cell (2003) [Pubmed]
  2. A kinase-cyclin pair in the RNA polymerase II holoenzyme. Liao, S.M., Zhang, J., Jeffery, D.A., Koleske, A.J., Thompson, C.M., Chao, D.M., Viljoen, M., van Vuuren, H.J., Young, R.A. Nature (1995) [Pubmed]
  3. Stress and developmental regulation of the yeast C-type cyclin Ume3p (Srb11p/Ssn8p). Cooper, K.F., Mallory, M.J., Smith, J.B., Strich, R. EMBO J. (1997) [Pubmed]
  4. Oxidative stress-induced destruction of the yeast C-type cyclin Ume3p requires phosphatidylinositol-specific phospholipase C and the 26S proteasome. Cooper, K.F., Mallory, M.J., Strich, R. Mol. Cell. Biol. (1999) [Pubmed]
  5. Saccharomyces cerevisiae C-type cyclin Ume3p/Srb11p is required for efficient induction and execution of meiotic development. Cooper, K.F., Strich, R. Eukaryotic Cell (2002) [Pubmed]
  6. Genetic analysis of the role of Pol II holoenzyme components in repression by the Cyc8-Tup1 corepressor in yeast. Lee, M., Chatterjee, S., Struhl, K. Genetics (2000) [Pubmed]
  7. Site-specific Srb10-dependent phosphorylation of the yeast Mediator subunit Med2 regulates gene expression from the 2-microm plasmid. Hallberg, M., Polozkov, G.V., Hu, G.Z., Beve, J., Gustafsson, C.M., Ronne, H., Björklund, S. Proc. Natl. Acad. Sci. U.S.A. (2004) [Pubmed]
  8. Kin28, the TFIIH-associated carboxy-terminal domain kinase, facilitates the recruitment of mRNA processing machinery to RNA polymerase II. Rodriguez, C.R., Cho, E.J., Keogh, M.C., Moore, C.L., Greenleaf, A.L., Buratowski, S. Mol. Cell. Biol. (2000) [Pubmed]
  9. The cyclin in the RNA polymerase holoenzyme is a target for the transcriptional repressor Tup1p in Saccharomyces cerevisiae. Schüller, J., Lehming, N. J. Mol. Microbiol. Biotechnol. (2003) [Pubmed]
  10. Cyclin-dependent protein kinase and cyclin homologs SSN3 and SSN8 contribute to transcriptional control in yeast. Kuchin, S., Yeghiayan, P., Carlson, M. Proc. Natl. Acad. Sci. U.S.A. (1995) [Pubmed]
  11. SSN genes that affect transcriptional repression in Saccharomyces cerevisiae encode SIN4, ROX3, and SRB proteins associated with RNA polymerase II. Song, W., Treich, I., Qian, N., Kuchin, S., Carlson, M. Mol. Cell. Biol. (1996) [Pubmed]
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