Repression of yeast Ste12 transcription factor by direct binding of unphosphorylated Kss1 MAPK and its regulation by the Ste7 MEK

  1. Lee Bardwell,
  2. Jeanette G. Cook1,
  3. Deepak Voora,
  4. Daniel M. Baggott,
  5. Anthony R. Martinez, and
  6. Jeremy Thorner2
  1. Department of Molecular and Cell Biology, Division of Biochemistry and Molecular Biology, University of California, Berkeley, California 94720 USA

Abstract

The mitogen-activated protein kinase (MAPK) Kss1 has a dual role in regulating filamentous (invasive) growth of the yeast Saccharomyces cerevisiae. The stimulatory function of Kss1 requires both its catalytic activity and its activation by the MAPK/ERK kinase (MEK) Ste7; in contrast, the inhibitory function of Kss1 requires neither. This study examines the mechanism by which Kss1 inhibits invasive growth, and how Ste7 action overcomes this inhibition. We found that unphosphorylated Kss1 binds directly to the transcription factor Ste12, that this binding is necessary for Kss1-mediated repression of Ste12, and that Ste7-mediated phosphorylation of Kss1 weakens Kss1–Ste12 interaction and relieves Kss1-mediated repression. Relative to Kss1, the MAPK Fus3 binds less strongly to Ste12 and is correspondingly a weaker inhibitor of invasive growth. Analysis of Kss1 mutants indicated that the activation loop of Kss1 controls binding to Ste12. Potent repression of a transcription factor by its physical interaction with the unactivated isoform of a protein kinase, and relief of this repression by activation of the kinase, is a novel mechanism for signal-dependent regulation of gene expression.

Keywords

Footnotes

  • 1 Present address: Department of Genetics, Duke University Medical Center, Durham, North Carolina 27710 USA.

  • 2 Corresponding author.

  • E-MAIL jeremy{at}socrates.berkeley.edu: FAX (510) 643-5035.

    • Received June 8, 1998.
    • Accepted July 24, 1998.
| Table of Contents

Life Science Alliance