scholarly journals Type V Myosin focuses the polarisome and shapes the tip of yeast cells

2020 ◽  
Author(s):  
Alexander Dünkler ◽  
Marcin Leda ◽  
Jan-Michael Kromer ◽  
Joachim Neller ◽  
Thomas Gronemeyer ◽  
...  
Keyword(s):  
Point Mutation ◽  
Filamentous Fungi ◽  
Actin Filaments ◽  
Yeast Cells ◽  
Secretory Vesicles ◽  
Biophysical Modeling ◽  
Multiple Copies ◽  
Molecular Forces ◽  
Type V ◽  
Compact Shape

AbstractThe polarisome is a cortical proteinaceous micro-compartment that organizes the growth of actin filaments and the fusion of secretory vesicles in yeasts and filamentous fungi. Polarisomes are compact, spot-like structures at the growing tips of their respective cells. The molecular forces that control form and size of this micro-compartment are not known. Here we identify a complex between the polarisome subunit Pea2 and the type V Myosin Myo2 that anchors Myo2 at the cortex of yeast cells. We discovered a point mutation in the cargo-binding domain of Myo2 that impairs the interaction with Pea2 and consequently the formation and focused localization of the polarisome. Cells carrying this mutation grow round instead of elongated buds. Further experiments and biophysical modeling suggest that polarisome nanoparticles use multiple copies of Myo2 and an actin filament polymerizing activity to drive the assembly of the polarisome and sustain its compact shape.

scholarly journals Type V myosin focuses the polarisome and shapes the tip of yeast cells

2021 ◽  
Vol 220 (5) ◽  
Author(s):  
Alexander Dünkler ◽  
Marcin Leda ◽  
Jan-Michael Kromer ◽  
Joachim Neller ◽  
Thomas Gronemeyer ◽  
...  
Keyword(s):  
Point Mutation ◽  
Filamentous Fungi ◽  
Actin Filaments ◽  
Binding Domain ◽  
Yeast Cells ◽  
Secretory Vesicles ◽  
Biophysical Modeling ◽  
Molecular Forces ◽  
Type V ◽  
Compact Shape

The polarisome is a cortical proteinaceous microcompartment that organizes the growth of actin filaments and the fusion of secretory vesicles in yeasts and filamentous fungi. Polarisomes are compact, spotlike structures at the growing tips of their respective cells. The molecular forces that control the form and size of this microcompartment are not known. Here we identify a complex between the polarisome subunit Pea2 and the type V Myosin Myo2 that anchors Myo2 at the cortex of yeast cells. We discovered a point mutation in the cargo-binding domain of Myo2 that impairs the interaction with Pea2 and consequently the formation and focused localization of the polarisome. Cells carrying this mutation grow round instead of elongated buds. Further experiments and biophysical modeling suggest that the interactions between polarisome-bound Myo2 motors and dynamic actin filaments spatially focus the polarisome and sustain its compact shape.

scholarly journals A formin-nucleated actin aster concentrates cell wall hydrolases for cell fusion in fission yeast

2015 ◽  
Vol 208 (7) ◽  
pp. 897-911 ◽  
Author(s):  
Omaya Dudin ◽  
Felipe O. Bendezú ◽  
Raphael Groux ◽  
Thierry Laroche ◽  
Arne Seitz ◽  
...  
Keyword(s):  
Cell Wall ◽  
Fission Yeast ◽  
Cell Fusion ◽  
Actin Filaments ◽  
Yeast Cells ◽  
Structured Illumination ◽  
Structured Illumination Microscopy ◽  
M Cell ◽  
Cell Wall Hydrolases ◽  
Type V

Cell–cell fusion is essential for fertilization. For fusion of walled cells, the cell wall must be degraded at a precise location but maintained in surrounding regions to protect against lysis. In fission yeast cells, the formin Fus1, which nucleates linear actin filaments, is essential for this process. In this paper, we show that this formin organizes a specific actin structure—the actin fusion focus. Structured illumination microscopy and live-cell imaging of Fus1, actin, and type V myosins revealed an aster of actin filaments whose barbed ends are focalized near the plasma membrane. Focalization requires Fus1 and type V myosins and happens asynchronously always in the M cell first. Type V myosins are essential for fusion and concentrate cell wall hydrolases, but not cell wall synthases, at the fusion focus. Thus, the fusion focus focalizes cell wall dissolution within a broader cell wall synthesis zone to shift from cell growth to cell fusion.

scholarly journals Spindle orientation in Saccharomyces cerevisiae depends on the transport of microtubule ends along polarized actin cables

2003 ◽  
Vol 161 (3) ◽  
pp. 483-488 ◽  
Author(s):  
Eric Hwang ◽  
Justine Kusch ◽  
Yves Barral ◽  
Tim C. Huffaker
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Actin Filaments ◽  
Yeast Cells ◽  
Similar Process ◽  
Spindle Orientation ◽  
Yeast Saccharomyces Cerevisiae ◽  
Cytoplasmic Microtubules ◽  
Actin Cables ◽  
Type V

Microtubules and actin filaments interact and cooperate in many processes in eukaryotic cells, but the functional implications of such interactions are not well understood. In the yeast Saccharomyces cerevisiae, both cytoplasmic microtubules and actin filaments are needed for spindle orientation. In addition, this process requires the type V myosin protein Myo2, the microtubule end–binding protein Bim1, and Kar9. Here, we show that fusing Bim1 to the tail of the Myo2 is sufficient to orient spindles in the absence of Kar9, suggesting that the role of Kar9 is to link Myo2 to Bim1. In addition, we show that Myo2 localizes to the plus ends of cytoplasmic microtubules, and that the rate of movement of these cytoplasmic microtubules to the bud neck depends on the intrinsic velocity of Myo2 along actin filaments. These results support a model for spindle orientation in which a Myo2–Kar9–Bim1 complex transports microtubule ends along polarized actin cables. We also present data suggesting that a similar process plays a role in orienting cytoplasmic microtubules in mating yeast cells.

scholarly journals Stoichiometry and compositional plasticity of the yeast nuclear pore complex revealed by quantitative fluorescence microscopy

2018 ◽  
Vol 115 (17) ◽  
pp. E3969-E3977 ◽  
Author(s):  
Sasikumar Rajoo ◽  
Pascal Vallotton ◽  
Evgeny Onischenko ◽  
Karsten Weis
Keyword(s):  
Nuclear Pore Complex ◽  
Yeast Cells ◽  
Nuclear Pore ◽  
Altered Expression ◽  
Copy Numbers ◽  
Quantitative Image ◽  
Multiple Copies ◽  
Almost All ◽  
High Degree

The nuclear pore complex (NPC) is an eightfold symmetrical channel providing selective transport of biomolecules across the nuclear envelope. Each NPC consists of ∼30 different nuclear pore proteins (Nups) all present in multiple copies per NPC. Significant progress has recently been made in the characterization of the vertebrate NPC structure. However, because of the estimated size differences between the vertebrate and yeast NPC, it has been unclear whether the NPC architecture is conserved between species. Here, we have developed a quantitative image analysis pipeline, termed nuclear rim intensity measurement (NuRIM), to precisely determine copy numbers for almost all Nups within native NPCs of budding yeast cells. Our analysis demonstrates that the majority of yeast Nups are present at most in 16 copies per NPC. This reveals a dramatic difference to the stoichiometry determined for the human NPC, suggesting that despite a high degree of individual Nup conservation, the yeast and human NPC architecture is significantly different. Furthermore, using NuRIM, we examined the effects of mutations on NPC stoichiometry. We demonstrate for two paralog pairs of key scaffold Nups, Nup170/Nup157 and Nup192/Nup188, that their altered expression leads to significant changes in the NPC stoichiometry inducing either voids in the NPC structure or substitution of one paralog by the other. Thus, our results not only provide accurate stoichiometry information for the intact yeast NPC but also reveal an intriguing compositional plasticity of the NPC architecture, which may explain how differences in NPC composition could arise in the course of evolution.

scholarly journals The Cooh-Terminal Domain of Myo2p, a Yeast Myosin V, Has a Direct Role in Secretory Vesicle Targeting

1999 ◽  
Vol 147 (4) ◽  
pp. 791-808 ◽  
Author(s):  
Daniel Schott ◽  
Jackson Ho ◽  
David Pruyne ◽  
Anthony Bretscher
Keyword(s):  
Secretory Vesicle ◽  
Restrictive Temperature ◽  
Secretory Vesicles ◽  
Tail Domain ◽  
Myosin V ◽  
Direct Role ◽  
Rab Protein ◽  
Polarized Delivery ◽  
Actin Cables ◽  
Type V

MYO2 encodes a type V myosin heavy chain needed for the targeting of vacuoles and secretory vesicles to the growing bud of yeast. Here we describe new myo2 alleles containing conditional lethal mutations in the COOH-terminal tail domain. Within 5 min of shifting to the restrictive temperature, the polarized distribution of secretory vesicles is abolished without affecting the distribution of actin or the mutant Myo2p, showing that the tail has a direct role in vesicle targeting. We also show that the actin cable–dependent translocation of Myo2p to growth sites does not require secretory vesicle cargo. Although a fusion protein containing the Myo2p tail also concentrates at growth sites, this accumulation depends on the polarized delivery of secretory vesicles, implying that the Myo2p tail binds to secretory vesicles. Most of the new mutations alter a region of the Myo2p tail conserved with vertebrate myosin Vs but divergent from Myo4p, the myosin V involved in mRNA transport, and genetic data suggest that the tail interacts with Smy1p, a kinesin homologue, and Sec4p, a vesicle-associated Rab protein. The data support a model in which the Myo2p tail tethers secretory vesicles, and the motor transports them down polarized actin cables to the site of exocytosis.

scholarly journals Two New Ypt GTPases Are Required for Exit From the Yeast trans-Golgi Compartment

1997 ◽  
Vol 137 (3) ◽  
pp. 563-580 ◽  
Author(s):  
Gregory Jedd ◽  
Jon Mulholland ◽  
Nava Segev
Keyword(s):  
Protein Transport ◽  
Small Gtpases ◽  
Yeast Cells ◽  
Secretory Vesicles ◽  
Golgi Compartment ◽  
Rab Family ◽  
Vacuolar Protein ◽  
Exocytic Pathway ◽  
Mutant Cells

Small GTPases of the Ypt/rab family are involved in the regulation of vesicular transport. These GTPases apparently function during the targeting of vesicles to the acceptor compartment. Two members of the Ypt/rab family, Ypt1p and Sec4p, have been shown to regulate early and late steps of the yeast exocytic pathway, respectively. Here we tested the role of two newly identified GTPases, Ypt31p and Ypt32p. These two proteins share 81% identity and 90% similarity, and belong to the same protein subfamily as Ypt1p and Sec4p. Yeast cells can tolerate deletion of either the YPT31 or the YPT32 gene, but not both. These observations suggest that Ypt31p and Ypt32p perform identical or overlapping functions. Cells deleted for the YPT31 gene and carrying a conditional ypt32 mutation exhibit protein transport defects in the late exocytic pathway, but not in vacuolar protein sorting. The ypt31/ 32 mutant secretory defect is clearly downstream from that displayed by a ypt1 mutant and is similar to that of sec4 mutant cells. However, electron microscopy revealed that while sec4 mutant cells accumulate secretory vesicles, ypt31/32 mutant cells accumulate aberrant Golgi structures. The ypt31/32 phenotype is epistatic to that of a sec1 mutant, which accumulates secretory vesicles. Together, these results indicate that the Ypt31/32p GTPases are required for a step that occurs in the transGolgi compartment, between the reactions regulated by Ypt1p and Sec4p. This step might involve budding of vesicles from the trans-Golgi. Alternatively, Ypt31/ 32p might promote secretion indirectly, by allowing fusion of recycling vesicles with the trans-Golgi compartment.

scholarly journals The α- and β′-COP WD40 Domains Mediate Cargo-selective Interactions with Distinct Di-lysine Motifs

2004 ◽  
Vol 15 (3) ◽  
pp. 1011-1023 ◽  
Author(s):  
Anne Eugster ◽  
Gabriella Frigerio ◽  
Martin Dale ◽  
Rainer Duden
Keyword(s):  
Endoplasmic Reticulum ◽  
Point Mutation ◽  
Yeast Cells ◽  
Golgi Compartment ◽  
Wd40 Domain ◽  
Golgi Protein ◽  
Overlapping Sets ◽  
Two Hybrid ◽  
Selective Interactions ◽  
In Cells

Coatomer is required for the retrieval of proteins from an early Golgi compartment back to the endoplasmic reticulum. The WD40 domain of α-COP is required for the recruitment of KKTN-tagged proteins into coatomer-coated vesicles. However, lack of the domain has only minor effects on growth in yeast. Here, we show that the WD40 domain of β′-COP is required for the recycling of the KTKLL-tagged Golgi protein Emp47p. The protein is degraded more rapidly in cells with a point mutation in the WD40 domain of β′-COP (sec27-95) or in cells lacking the domain altogether, whereas a point mutation in the Clathrin Heavy Chain Repeat (sec27-1) does not affect the turnover of Emp47p. Lack of the WD40 domain of β′-COP has only minor effects on growth of yeast cells; however, absence of both WD40 domains of α- and β′-COP is lethal. Two hybrid studies together with our analysis of the maturation of KKTN-tagged invertase and the turnover of Emp47p in α- and β′-COP mutants suggest that the two WD40 domains of α- and β′-COP bind distinct but overlapping sets of di-lysine signals and hence both contribute to recycling of proteins with di-lysine signals.

scholarly journals Molecular analysis of GPH1, the gene encoding glycogen phosphorylase in Saccharomyces cerevisiae.

1989 ◽  
Vol 9 (4) ◽  
pp. 1659-1666 ◽  
Author(s):  
P K Hwang ◽  
S Tugendreich ◽  
R J Fletterick
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Glycogen Phosphorylase ◽  
Glucose Repression ◽  
Essential Gene ◽  
Yeast Cells ◽  
Exponential Growth Phase ◽  
Phosphorylase Activity ◽  
Glycogen Accumulation ◽  
Multiple Copies ◽  
Diploid Cells

In yeast cells, the activity of glycogen phosphorylase is regulated by cyclic AMP-mediated phosphorylation of the enzyme. We have previously cloned the gene for glycogen phosphorylase (GPH1) in Saccharomyces cerevisiae. To assess the role of glycogen and phosphorylase-catalyzed glycogenolysis in the yeast life cycle, yeast strains lacking a functional GPH1 gene or containing multiple copies of the gene were constructed. GPH1 was found not to be an essential gene in yeast cells. Haploid cells disrupted in GPH1 lacked phosphorylase activity and attained higher levels of intracellular glycogen but otherwise were similar to wild-type cells. Diploid cells homozygous for the disruption were able to sporulate and give rise to viable ascospores. Absence of functional GPH1 did not impair cells from synthesizing and storing trehalose. Increases in phosphorylase activity of 10- to 40-fold were detected in cells carrying multiple copies of GPH1-containing 2 microns plasmid. Northern (RNA) analysis indicated that GPH1 transcription was induced at the late exponential growth phase, almost simultaneous with the onset of intracellular glycogen accumulation. Thus, the low level of glycogen in exponential cells was not primarily maintained through regulating the phosphorylation state of a constitutive amount of phosphorylase. GPH1 did not appear to be under formal glucose repression, since transcriptional induction occurred well in advance of glucose depletion from the medium.

scholarly journals Yeast-to-Hyphal Transition Triggers Formin-dependent Golgi Localization to the Growing Tip inCandida albicans

2006 ◽  
Vol 17 (10) ◽  
pp. 4364-4378 ◽  
Author(s):  
Padmashree C.G. Rida ◽  
Akiko Nishikawa ◽  
Gena Y. Won ◽  
Neta Dean
Keyword(s):  
Filamentous Fungi ◽  
Cell Body ◽  
Structural Integrity ◽  
Distal Portion ◽  
Distal Region ◽  
Yeast Cells ◽  
Long Distance ◽  
Golgi Localization ◽  
Hyphal Formation ◽  
Membrane Components

Rapid and long-distance secretion of membrane components is critical for hyphal formation in filamentous fungi, but the mechanisms responsible for polarized trafficking are not well understood. Here, we demonstrate that in Candida albicans, the majority of the Golgi complex is redistributed to the distal region during hyphal formation. Randomly distributed Golgi puncta in yeast cells cluster toward the growing tip during hyphal formation, remain associated with the distal portion of the filament during its extension, and are almost absent from the cell body. This restricted Golgi localization pattern is distinct from other organelles, including the endoplasmic reticulum, vacuole and mitochondria, which remain distributed throughout the cell body and hypha. Hyphal-induced positioning of the Golgi and the maintenance of its structural integrity requires actin cytoskeleton, but not microtubules. Absence of the formin Bni1 causes a hyphal-specific dispersal of the Golgi into a haze of finely dispersed vesicles with a sedimentation density no different from that of normal Golgi. These results demonstrate the existence of a hyphal-specific, Bni1-dependent cue for Golgi integrity and positioning at the distal portion of the hyphal tip, and suggest that filamentous fungi have evolved a novel strategy for polarized secretion, involving a redistribution of the Golgi to the growing tip.

scholarly journals Membrane association and functional regulation of Sec3 by phospholipids and Cdc42

2008 ◽  
Vol 180 (1) ◽  
pp. 145-158 ◽  
Author(s):  
Xiaoyu Zhang ◽  
Kelly Orlando ◽  
Bing He ◽  
Fengong Xi ◽  
Jian Zhang ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Yeast Cells ◽  
Membrane Association ◽  
Secretory Vesicles ◽  
Cell Morphogenesis ◽  
Guanosine Triphosphate ◽  
Polarized Cell Growth ◽  
N Terminus ◽  
Functional Regulation ◽  
Key Residues

The exocyst is an octameric protein complex implicated in tethering post-Golgi secretory vesicles at the plasma membrane in preparation for fusion. However, it is not clear how the exocyst is targeted to and physically associates with specific domains of the plasma membrane and how its functions are regulated at those regions. We demonstrate that the N terminus of the exocyst component Sec3 directly interacts with phosphatidylinositol 4,5-bisphosphate. In addition, we have identified key residues in Sec3 that are critical for its binding to the guanosine triphosphate–bound form of Cdc42. Genetic analyses indicate that the dual interactions of Sec3 with phospholipids and Cdc42 control its function in yeast cells. Disrupting these interactions not only blocks exocytosis and affects exocyst polarization but also leads to defects in cell morphogenesis. We propose that the interactions of Sec3 with phospholipids and Cdc42 play important roles in exocytosis and polarized cell growth.

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