A protein interaction map for cell polarity development

Many genes required for cell polarity development in budding yeast have been identified and arranged into a functional hierarchy. Core elements of the hierarchy are widely conserved, underlying cell polarity development in diverse eukaryotes. To enumerate more fully the protein–protein interactions that mediate cell polarity development, and to uncover novel mechanisms that coordinate the numerous events involved, we carried out a large-scale two-hybrid experiment. 68 Gal4 DNA binding domain fusions of yeast proteins associated with the actin cytoskeleton, septins, the secretory apparatus, and Rho-type GTPases were used to screen an array of yeast transformants that express ∼90% of the predicted Saccharomyces cerevisiae open reading frames as Gal4 activation domain fusions. 191 protein–protein interactions were detected, of which 128 had not been described previously. 44 interactions implicated 20 previously uncharacterized proteins in cell polarity development. Further insights into possible roles of 13 of these proteins were revealed by their multiple two-hybrid interactions and by subcellular localization. Included in the interaction network were associations of Cdc42 and Rho1 pathways with proteins involved in exocytosis, septin organization, actin assembly, microtubule organization, autophagy, cytokinesis, and cell wall synthesis. Other interactions suggested direct connections between Rho1- and Cdc42-regulated pathways; the secretory apparatus and regulators of polarity establishment; actin assembly and the morphogenesis checkpoint; and the exocytic and endocytic machinery. In total, a network of interactions that provide an integrated response of signaling proteins, the cytoskeleton, and organelles to the spatial cues that direct polarity development was revealed

The similarity of life across the universe

Is the hypothesis correct that if life exists elsewhere in the universe, it would have forms and structures unlike anything we could imagine? From the subatomic level in cellular energy acquisition to the assembly and even behavior of organisms at the scale of populations, life on Earth exhibits characteristics that suggest it is a universal norm for life at all levels of hierarchy. These patterns emerge from physical and biochemical limitations. Their potentially universal nature is supported by recent data on the astrophysical abundance and availability of carbon compounds and water. Within these constraints, biochemical and biological variation is certainly possible, but it is limited. If life exists elsewhere, life on Earth, rather than being a contingent product of one specific experiment in biological evolution, is likely to reflect common patterns for the assembly of living matter

Zds2p Regulates Swe1p-dependent Polarized Cell Growth in Saccharomyces cerevisiae via a Novel Cdc55p Interaction Domain

A C-terminal region in Zds2p (ZH4) is required for regulation of Swe1p-dependent polarized cell growth and this region is necessary and sufficient for interaction with protein phosphatase 2A regulatory subunit, Cdc55p. Our results indicate that the Zds proteins regulate the Swe1p-dependent G2/M checkpoint in a CDC55-dependent manner

EM immunogold localization of Cdc42p in <i>sec6-4^ts</i> cells.

<p>EM immunogold localization of Cdc42p (A) or Rho1p (D) in log-phase <i>sec6-4</i> cells shifted to 37°C for 60 min. B and E) Distribution of gold particles among various membrane compartments within buds of the same preparations shown in (A) and (D) when probed for Cdc42p (B; n = 37 cells) or Rho1p (E; n = 33 cells). PM, plasma membrane; V, 80–100 nm diameter vesicles; ER, endoplasmic reticulum; ER-PM, endoplasmic reticulum and/or plasma membrane; ER-V, endoplasmic reticulum and/or vesicles; V-PM, vesicles and/or plasma membrane; UN (unassigned), membrane compartment of ambiguous identity. C and F) Average number of gold particles within the bud and mother of the same cell, scored on the same section, standardized to an area of 1 um². Error bars indicate SEM. Cells and sections scored in (C and F) are the same as those scored in (B and E), respectively.</p

Co-purification of Cdc42p with low density, Sec4p-marked vesicles.

<p>A) Immunoblots of 100,000×<i>g</i> pellets of fractions collected from an 18–34% Nycodenz-sorbitol buoyant density gradient loaded with extracts prepared from equivalent OD₆₀₀ units of <i>sec6-4^ts</i> cells grown at 25°C or 37°C for 90 min. Each lane was loaded equivalent fraction volumes and, for the same probe, incubated with antibody of equivalent titer for the same amount of time. All blots are from the same fractionation, with the Sec4p and Bgl2p panels reprinted with permission from Alfaro <i>et al</i>. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0099494#pone.0099494-Alfaro1" target="_blank">[37]</a> © 2011 <i>Traffic</i>. All blots at an indicated temperature were prepared from the same fractions from the same gradient. B) Graph showing invertase activity across “37°C” buoyant density gradient shown in (A) and sucrose density across an unloaded gradient processed in parallel. Fraction densities were calculated based on a standard curve of Nycodenz-sorbitol concentration versus refractive index. C) Thin section electron micrographs showing vesicle association with a M500 Dynabead coated with mouse monoclonal anti-Sec4p antibody (left), but not with the same type of bead coated with mouse IgG (right), after incubation with a pooled, Sec4p-enriched, buoyant-density gradient fraction from <i>sec6-4^ts</i> cells grown at 37°C for 90 min (comparable to fractions 11–14 in (A)). D) Immunoblots of a pooled, Sec4p-enriched, low-density gradient fraction (S), after incubation with Protein G-Dynabeads (P) coated with a monoclonal antibody against Sec4p or mouse IgG, and probed for plasma membrane marker Pma1p or post-Golgi secretory vesicle marker Sec4p. E) Immunoblots of pooled, Sec4p-enriched, low-density gradient fraction (S), after incubation with Dynabeads coated with a monoclonal antibody against Sec4p or Pma1p (P), probed for Cdc42p or Sec4p. In (D) and (E), the stoichiometric ratio of pellet to supernatant is 20∶1.</p