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Light-mediated Reversible Modulation of the Mitogen-activated Protein Kinase Pathway during Cell Differentiation and Xenopus Embryonic Development
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Activation of the Smk1 mitogen-activated protein kinase by developmentally regulated autophosphorylation

Elizabeth Whinston1, Gregory Omerza, Amrita Singh

  • 1Department of Biochemistry and Molecular Biology, Thomas Jefferson University, Philadelphia, Pennsylvania, USA.

Molecular and Cellular Biology
|December 5, 2012
PubMed

Insights

Cyclin-dependent kinase-activating kinase (Cak1) and meiosis-specific protein Ssp2 regulate the activity of the Smk1 mitogen-activated protein kinase (MAPK) during yeast sporulation, controlling spore development.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Biochemistry

Background:

  • Smk1 (Saccharomyces cerevisiae) is a meiosis-specific mitogen-activated protein kinase (MAPK) crucial for spore morphogenesis.
  • MAPKs are typically regulated by dual phosphorylation of a T-X-Y motif, but Smk1's regulation deviates from this standard pathway.

Purpose of the Study:

  • To elucidate the specific mechanisms regulating Smk1 activity during meiosis.
  • To identify the kinases responsible for phosphorylating Smk1's activation motif.
  • To understand how Smk1 activity is temporally controlled during sporulation.

Main Methods:

  • Investigated the phosphorylation of Smk1's T-X-Y activation motif using biochemical assays.
  • Utilized genetic manipulation in Saccharomyces cerevisiae to study the roles of Cak1 and Ssp2.
  • Analyzed the temporal expression patterns of Smk1 and Ssp2 proteins during meiosis.

Main Results:

  • The T residue in Smk1's activation motif is phosphorylated by cyclin-dependent kinase (CDK)-activating kinase, Cak1.
  • The Y residue is autophosphorylated via an intramolecular reaction dependent on the meiosis-specific protein Ssp2.
  • Smk1 protein accumulates before Ssp2, leading to a low-activity (pT) form early and a high-activity (pT/pY) form later in sporulation.

Conclusions:

  • Cak1 and Ssp2 provide a novel regulatory mechanism for Smk1 activity, distinct from canonical MAPK activation.
  • Ssp2's requirement during Smk1 production suggests a role in activating a transitional Smk1 intermediate.
  • This study reveals how Smk1 activity thresholds are generated and offers insights into coupling MAPK signaling to developmental programs.

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