Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.2.1.26 (invertase)
 4,927 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have recently shown that actin and fimbrin are required for the internalization step of endocytosis in yeast. Using a yeast strain with a temperature-sensitive allele of CMD1, encoding calmodulin, we demonstrate that this protein is also required for this process. Calmodulin mutants that have lost their high-affinity calcium binding sites are, however, able to carry out endocytosis normally. A mutation in Myo2p, an unconventional myosin that is a possible target of calmodulin, did not inhibit endocytosis. The function of calmodulin in endocytosis seems to be specific among membrane trafficking events, because the calmodulin mutants are not defective for biogenesis of soluble vacuolar hydrolases nor invertase secretion. Calmodulin does not seem to play a major role in the post-internalization steps of the endocytic pathway in yeast.
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PMID:Calcium-independent calmodulin requirement for endocytosis in yeast. 798 51

We examined the effects of yeast actin NH2-terminal mutations on actomyosin interactions and the function of actin in vivo through measurements of actin-activated ATPase activity, cosedimentation with rabbit muscle myosin subfragment 1 (S-1), in vitro motility, and invertase secretion assays. As reported earlier (Cook, R. K., Blake, W., and Rubenstein, P. A. (1992) J. Biol. Chem. 267, 9430-9436), elimination of NH2-terminal acidic residues from yeast actin results in an increased actin bundling, decreased actin-activated S-1 ATPase, and complete inhibition of actin filament sliding over myosin. Here we show that the addition of 2 new acidic residues to the NH2 terminus of yeast actin increased the Vmax value and the catalytic efficiency of the actin-activated ATPase activity of S-1. However, the binding of actin to S-1 in the presence of ATP and the velocities of actin sliding over myosin in the in vitro motility assays were not affected by this mutation. Thus, the number of actin NH2-terminal negative charges is important for actin activation of myosin S-1 ATPase activity, while only a minimum number of acidic residues is required for actin sliding over myosin in vitro. The number of actin NH2-terminal negative charges therefore appears to determine the efficiency with which the energy from ATP hydrolysis is converted to filament sliding.
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PMID:Enhanced stimulation of myosin subfragment 1 ATPase activity by addition of negatively charged residues to the yeast actin NH2 terminus. 842 14

A screen was designed to identify temperature-sensitive mutants of Saccharomyces cerevisiae, whose transcription of both ribosomal RNA and ribosomal protein genes is repressed at the nonpermissive temperature. The gene from one such mutant was cloned by complementation. The gene encodes a predicted product that is nearly 65% identical to the human GTPase, Rab6, and is likely to be identical to the yeast gene YPT6. It is essential for growth only at elevated temperatures. The mutant strain is partially defective in the maturation of the vacuolar protein carboxypeptidase Y, as well as in the secretion of invertase, which accumulates as a core-glycosylated form characteristic of the endoplasmic reticulum or the cis-Golgi, suggesting that Ypt6p is involved in an early step of the secretory pathway, earlier than that reported for the mammalian Rab6. The mutant protein, a truncation at codon 64 of 215, has a stronger phenotype than the null allele of YPT6. Four other mutants selected for defective ribosome synthesis at the nonpermissive temperature were also found to have defects in carboxypeptidase Y maturation, giving emphasis to our previous finding that a functional secretory pathway is essential for continued ribosome synthesis. Cloning of extragenic suppressors of the ts allele of YPT6 has revealed two additional proteins that influence the secretory pathway: Ssd1p, a suppressor of many mutations, and Imh1p, which bears some homology to the C-terminal portion of the cytoskeletal proteins integrin and myosin.
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PMID:Mutation of the Rab6 homologue of Saccharomyces cerevisiae, YPT6, inhibits both early Golgi function and ribosome biosynthesis. 866 25

The organization of the actin cytoskeleton plays a critical role in cell physiology in motile and nonmotile organisms. Nonetheless, the function of the actin based motor molecules, members of the myosin superfamily, is not well understood. Deletion of MYO3, a yeast gene encoding a "classic" myosin I, has no detectable phenotype. We used a synthetic lethality screen to uncover genes whose functions might overlap with those of MYO3 and identified a second yeast myosin 1 gene, MYO5. MYO5 shows 86 and 62% identity to MYO3 across the motor and non-motor regions. Both genes contain an amino terminal motor domain, a neck region containing two IQ motifs, and a tail domain consisting of a positively charged region, a proline-rich region containing sequences implicated in ATP-insensitive actin binding, and an SH3 domain. Although myo5 deletion mutants have no detectable phenotype, yeast strains deleted for both MYO3 and MYO5 have severe defects in growth and actin cytoskeletal organization. Double deletion mutants also display phenotypes associated with actin disorganization including accumulation of intracellular membranes and vesicles, cell rounding, random bud site selection, sensitivity to high osmotic strength, and low pH as well as defects in chitin and cell wall deposition, invertase secretion, and fluid phase endocytosis. Indirect immunofluorescence studies using epitope-tagged Myo5p indicate that Myo5p is localized at actin patches. These results indicate that MYO3 and MYO5 encode classical myosin I proteins with overlapping functions and suggest a role for Myo3p and Myo5p in organization of the actin cytoskeleton of Saccharomyces cerevisiae.
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PMID:Synthetic lethality screen identifies a novel yeast myosin I gene (MYO5): myosin I proteins are required for polarization of the actin cytoskeleton. 868 64

F-actin and associated myosins are thought to take part in a wide range of cellular processes, like motility and contraction, polarized growth, and secretion. The reagent 2,3-butanedione monoxime (BDM) is a well characterized inhibitor of the contraction of vertebrate muscle that reversibly affects myosin function and influences the intracellular concentration of Ca2+. Here we describe the influence of BDM on growth and division of the fission yeast Schizosaccharomyces pombe. At concentrations from 1-30 mM, BDM gradually inhibited formation and growth of S. pombe colonies on agar plates, with a lethal effect at > or = 15 mM. In strains of S. pombe that were blocked by elevated temperature from entry into mitosis, drug treatment reversibly decreased microtubule-independent tip growth and septation, with an IC50 value around 12 mM; nuclear division, on the other hand, was essentially unaffected by up to 15 mM BDM. At 30 mM BDM the secretion of invertase, which required both F-actin and microtubules, was decreased to the same extent as that seen when cytochalasin D was used to disrupt F-actin. However, the actin cytoskeleton was insensitive to up to 10 mM BDM, while the actin patches lost their polar distribution at 20-30 mM BDM. Cells treated with 5-20 mM BDM for 3 hours and then high pressure frozen did not show an accumulation of secretory vesicles. However, 10 mM BDM treatment disorganized the fungal cell wall, resulting in some unusually thick parts lying next to regions were the wall was almost absent. These defects could be rescued by incubating the cells in inhibitors of glucanases. Osmolytic stabilization with sorbitol rescued the effect of 15 mM BDM on colony survival, indicating that the secretion of wall components and/or wall-modifying enzymes may be the principal reason for cell death caused by BDM. Our results are consistent with the hypothesis that BDM influences actin-dependent processes in fission yeast and that actomyosin-dependent motility contributes to the secretory process of tip growth.
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PMID:Effects of the myosin inhibitor 2,3-butanedione monoxime on the physiology of fission yeast. 993 Jun 53