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  • The EMBO Journal (2001) 20, 1123 - 1133
  • doi:10.1093/emboj/20.5.1123

Regulation of the Sko1 transcriptional repressor by the Hog1 MAP kinase in response to osmotic stress

Markus Proft1, Amparo Pascual-Ahuir1, Eulàlia de Nadal2, Joaquin Ariño3, Ramón Serrano1 and Francesc Posas2

  1. Instituto de Biología Molecular y Celular de Plantas, Universidad Politécnica de Valencia-CSIC, 46022 Valencia, Spain
  2. Cell Signaling Unit, Departament de Ciències Experimentals i de la Salut, Universitat Pompeu Fabra (UPF), E-08003 Barcelona, Spain
  3. Departament de Bioquímica i Biologia Molecular, Facultat de Veterinària, Universitat Autònoma de Barcelona, E-08193 Barcelona, Spain

Correspondence to:

Francesc Posas, E-mail: francesc.posas@cexs.upf.es

Received 11 October 2000; Accepted 5 January 2001; Revised 8 November 2000

Exposure of yeast to increases in extracellular osmolarity activates the Hog1 mitogen-activated protein kinase (MAPK), which is essential for the induction of gene expression required for cell survival upon osmotic stress. Several genes are regulated in response to osmotic stress by Sko1, a transcriptional repressor of the ATF/CREB family. We show by in vivo coprecipitation and phosphorylation studies that Sko1 and Hog1 interact and that Sko1 is phosphorylated upon osmotic stress in a Hog1-dependent manner. Hog1 phosphorylates Sko1 in vitro at multiple sites within the N-terminal region. Phosphorylation of Sko1 disrupts the Sko1–Ssn6–Tup1 repressor complex, and consistently, a mutant allele of Sko1, unphosphorylatable by Hog1, exhibits less derepression than the wild type. Interestingly, Sko1 repressor activity is further enhanced in strains with high protein kinase A (PKA) activity. PKA phosphorylates Sko1 near the bZIP domain and mutation of these sites eliminates modulation of Sko1 responses to high PKA activity. Thus, Sko1 transcriptional repression is controlled directly by the Hog1 MAPK in response to stress, and this effect is further modulated by an independent signaling mechanism through the PKA pathway.

  • Keywords:

    • Hog1,
    • mitogen-activated protein kinase,
    • signal transduction,
    • Sko1,
    • stress response