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Journal of Cell Science, Vol 113, Issue 1 153-160, Copyright © 2000 by Company of Biologists
JOURNAL ARTICLES |
R Loewith, A Hubberstey and D Young
Department of Biochemistry and Molecular Biology, University of Calgary Health Sciences Centre, Calgary, Alberta, T2N4N1, Canada.
We previously reported the identification of Mkh1, a MEK kinase in Schizosaccharomyces pombe that is required for cell wall integrity, and we presented genetic evidence that Pmk1/Spm1, a MAP kinase, functions downstream from Mkh1 in the same pathway. Here, we report the identification of Skh1, a MEK (MAP kinase kinase) in S. pombe. The sequence of Skh1 is nearly identical to that of the recently reported Pek1 sequence. We present biochemical and genetic evidence that Skh1 is the MEK component of the Mkh1-Spm1 MAP kinase cascade. Our yeast two-hybrid results indicate that Mkh1, Skh1, and Spm1 physically interact to form a ternary complex. Deletion of mkh1, skh1 or spm1 results in identical phenotypes, including sensitivity to (beta)-glucanase treatment, growth inhibition on media containing KCl, and filamentous growth on medium containing caffeine. Double mutant strains exhibit phenotypes that are identical to the single mutant strains. Furthermore, expression of an activated HA-Skh1(DD )protein suppressed these defects in mkh1(delta) cells, and overexpression of Spm1 suppressed these defects in skh1(delta) cells. We also show that HA-Spm1 is hyper-phosphorylated on tyrosine residues in cells co-expressing the activated HA-Skh1(DD) protein. Furthermore, we found the phosphorylated/activated form of GFP-HA-Spm1 at detectable levels in wild-type cells, but not at appreciable levels in mkh1(delta) or skh1(delta) cells expressing this fusion protein. Together, our results indicate that Mkh1, Skh1 and Spm1 constitute a MAPK cascade in fission yeast.
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 T. Y. Huang, M. Renaud-Young, and D. Young Nak1 interacts with Hob1 and Wsp1 to regulate cell growth and polarity in Schizosaccharomyces pombe J. Cell Sci., January 1, 2005; 118(1): 199 - 210. [Abstract] [Full Text] [PDF]
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T. Y. Huang, N. A. Markley, and D. Young Nak1, an Essential Germinal Center (GC) Kinase Regulates Cell Morphology and Growth in Schizosaccharomyces pombe J. Biol. Chem., January 3, 2003; 278(2): 991 - 997. [Abstract] [Full Text] [PDF]
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M. J. Jang, M. Jwa, J.-H. Kim, and K. Song Selective Inhibition of MAPKK Wis1 in the Stress-activated MAPK Cascade of Schizosaccharomyces pombe by Novel Berberine Derivatives J. Biol. Chem., March 29, 2002; 277(14): 12388 - 12395. [Abstract] [Full Text] [PDF]
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M. Meijer, F. Karimi-Busheri, T. Y. Huang, M. Weinfeld, and D. Young Pnk1, a DNA Kinase/Phosphatase Required for Normal Response to DNA Damage by gamma -Radiation or Camptothecin in Schizosaccharomyces pombe J. Biol. Chem., February 1, 2002; 277(6): 4050 - 4055. [Abstract] [Full Text] [PDF]
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A. Bandyopadhyay, T. Matsumoto, and U. Maitra Fission Yeast Int6 Is Not Essential for Global Translation Initiation, but Deletion of int6+ Causes Hypersensitivity to Caffeine and Affects Spore Formation Mol. Biol. Cell, November 1, 2000; 11(11): 4005 - 4018. [Abstract] [Full Text]
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