Section: Figures

Peter Pryciak, Ph.D.

Academic Role: Associate Professor

Faculty Appointment(s) In:
   Molecular Genetics and Microbiology

Other Affiliation(s):
   Cell Dynamics Group
   Interdisciplinary Graduate Program

Figures

Figure 1.   (A) Yeast mating reaction. Mating pheromones (a factor and a factor) cause cells to stop dividing, polarize toward their mating partners, and fuse with each other to form a diploid zygote.  (B) Pheromone response pathway, emphasizing the membrane recruitment of the "scaffold" protein, Ste5, by the heterotrimeric G proteinbg dimer.  This allows activation of the MAP kinase cascade.

Figure 2.   (A) Synergy between two weak interactions contols Ste5 membrane recruitment.  (B) The Ste5 PM domain is a putative amphipathic alpha helix that binds acidic phospholipid membranes in vivo and in vitro.  (C) Model for CDK inhibition of signaling through the mating MAP kinase pathway.  Phosphorylation of multiple sites flanking the PM domain electrostatically interferes with membrane binding, and hence disrupts signaling.  The inset at bottom shows cell cycle-dependent fluctuations in the electrophoretic mobility of Ste5, indicative of periodic phosphorylation.

Figure 3.  Regulation and localization of Cdc42 targets.  (A) The PAK-family kinase Ste20 is localized and activated by the GTPase Cdc42.  Our recent results show that this also requires direct membrane interaction by Ste20.  (B) Localization of isolated membrane-binding motifs called BR domains (for "basic-rich") from three different Cdc42 targets.  (C) Domain structure of yeast Cdc42 targets, illustrating the presence of a membrane-binding motif (BR or PH domain) immediately adjacent to the Cdc42-binding motif in each protein.

Figure 4.   (A) Yeast cell polarization in response to pheromone.  A gradient of pheromone normally serves as a spatial cue for the direction of polarization; cells polarize up the chemoattractant gradient in order to find mating partners.  However, these cells can polarize in random directions when exposed to a uniform field of chemoattractant, implying the existence of "symmetry breaking" mechanisms that can generate asymmetric responses to symmetric signals, and "directional persistence" mechanisms that allow for continual reinforcement of the initially chosen direction.  (B) Common components are shared among three separate signaling pathways: mating, filamentous growth, and the high osmolarity glycerol (HOG) response.  Though individual proteins are shared (e.g., Cdc42, Ste20, Ste50, Ste11), these pathways are insulated from each other so that each stimulus activates only a single pathway.  Pathway-specific scaffold proteins such as Ste5 and Pbs2 are thought to help provide this insulation.  (In contrast, no known scaffold exists for the filamentation pathway.)  Membrane-localized assembly can also contribute to signaling fidelity, by limiting phosphorylation events to those substrates that are co-localized with the active signaling complex.

Office: Bio IV Rm# 330
Phone: 508-856-8756
E-mail: Peter.Pryciak@umassmed.edu
Keywords: Signal Transduction, Cell Dynamics, Yeast, Cell Biology, Genetics

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