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  • 1
    ISSN: 0749-503X
    Keywords: AFT1 ; transcriptional factor ; iron uptake ; phosphorylation ; respiratory growth ; Life and Medical Sciences ; Genetics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: High-affinity iron uptake in Saccharomyces cerevisiae involves the extracytoplasmic reduction of ferric ions by FRE1 and FRE2 reductases. Ferrous ions are then transported across the plasma membrane through the FET3 oxidase-FTR1 permease complex. Expression of the high-affinity iron uptake genes is induced upon iron deprivation. We demonstrate that AFT1 is differentially involved in such regulation. Aft1 protein is required for maintaining detectable non-induced levels of FET3 expression and for induction of FRE2 in iron starvation conditions. On the contrary, FRE1 mRNA induction is normal in the absence of Aft1, although the existence of AFT1 point mutations causing constitutive expression of FRE1 (Yamaguchi-Iwai et al., EMBO J. 14: 1231-1239, 1995) indicates that Aft1 may also participate in FRE1 expression in a dispensable way. The alterations in the basal levels of expression of the high-affinity iron uptake genes may explain why the AFT1 mutant is unable to grow on respirable carbon sources. Overexpression of AFT1 leads to growth arrest at the G1 stage of the cell cycle. Aft1 is a transcriptional activator that would be part of the different transcriptional complexes interacting with the promoter of the high-affinity iron uptake genes. Aft1 displays phosphorylation modifications depending on the growth stage of the cells, and it might link induction of genes for iron uptake to other metabolically dominant requirements for cell growth. © John Wiley & Sons, Ltd.
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Yeast 7 (1991), S. 1-14 
    ISSN: 0749-503X
    Keywords: Saccharomyces cerevisiae ; cell cycle ; budding ; spore germination ; Life and Medical Sciences ; Genetics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: Cloning and sequencing of RCS1, a Saccharomyces cerevisiae gene whose product seems to be involved in timing the budding event of the cell cycle, is described. A haploid strain in which the 3′-terminal region of the chromosomal copy of the gene has been disrupted produces cells that are, on average, twice the size of cells of the parental strain. The critical size for budding in the mutant is similarly increased, and the disruption mutation is dominant in a diploid heterozygous for the RCS1 gene. Spores from this diploid have a reduced ability to germinate, the effect being more pronounced in the spores carrying the disrupted copy of RCS1. However, disrupted cells recover from α-factor treatment equally as well as wild-type cells.
    Additional Material: 4 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Yeast 8 (1992), S. 107-115 
    ISSN: 0749-503X
    Keywords: Yeast ; Saccharomyces cerevisiae ; glycolysis ; hexokinase ; phosphofructokinase ; Life and Medical Sciences ; Genetics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: The enzymatic steps involved in the inhibition of glycolysis by 2-deoxygalactose in Saccharomyces cerevisiae have been investigated. Yeast, incubated with 2-deoxygalactose, accumulates up to 8 mM-2-deoxygalactose, 30 mM-2-deoxygalactose-1-phosphate and 0·25 mM-UDP-2-deoxygalactose and UDP-2-dexyglucose. An inverse correlation between 2-deoxygalactose-1-phosphate content and rate of glycolysis has been observed. The intracellular concentration of glycolytic intermediates and related metabolites point to the hexokinase and phosphofructokinase steps as the targets for the inhibition of glycolysis by 2-deoxygalactose and rule out all other mechanisms that have been proposed to explain this inhibition.
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Yeast 13 (1997), S. 541-549 
    ISSN: 0749-503X
    Keywords: cytoskeleton ; endocytosis ; yeast maltose transporter ; Saccharomyces cerevisiae ; Life and Medical Sciences ; Genetics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: Certain components of the cytoskeleton play a role in yeast fluid-phase endocytosis as well as in endocytosis of the α-factor when this pheromone is bound to its 7-transmembrane segment receptor. The yeast maltose transporter is a 12-transmembrane segment protein that, under certain physiological conditions, is degraded in the vacuole after internalization by endocytosis. In this work, the possible role of the cytoskeleton in endocytosis of this transporter has been investigated. Using mutants defective in β-tubulin, actin and the actin-binding proteins Sac6 and Abp85, as well as nocodazole, which inhibits formation of microtubules, we have shown that actin microfilaments are involved in endocytosis of the maltose transporter whereas microtubules are not.© 1997 John Wiley & Sons, Ltd.
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  • 5
    ISSN: 0749-503X
    Keywords: dolichol-PP-GlcNAc2 ; translocation ; endoplasmic reticulum ; alg1 ; exoglucanase ; S. cerevisiae ; Life and Medical Sciences ; Genetics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: Transfer of truncated oligosaccharides to yeast exoglucanase (Exg) in Saccharomyces cerevisiae alg1 has been investigated. When incubated at the non-permissive temperature, alg1 cells secreted into the culture medium, in addition to the exoglucanase glycoforms secreted by wild type, underglycosylated forms as well as material with ionic properties of the non-glycosylated enzyme. As expected, none of the latter had affinity towards concanavalin A, but part of it bound to wheat germ agglutinin (WGA), suggesting that it contained, in addition to non-glycosylated Exg, glycoforms carrying non-reducing terminal GlcNAc. Only the WGA-bound material could be labelled with galactosyltransferase; furthermore, the label could be released by treatment with peptide-N4-N-acetyl-β-glucosamine asparagine amidase. These results unambiguously demonstrate that GlcNAc2 can be transferred from dolichol-PP-GlcNAc2 to one or both sequons of yeast Exg. Accordingly, they support previous observations suggesting that this early intermediate is able to translocate in vivo in order to make its sugar portion accessible to the oligosaccharyltransferase in the lumen of the endoplasmic reticulum. © 1998 John Wiley & Sons, Ltd.
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  • 6
    ISSN: 0730-2312
    Keywords: anti-idiotypic antibodies ; thyrotropin subunits ; thyrotropin receptor ; monoclonal antibody ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: TSH is a heterodimeric glycoprotein hormone, whose dissociated subunits are without biological activity. This has precluded the assessment of the relative contribution of each subunit to hormone action. We have raised anti-idiotypes to monoclonal antibodies specific, respectively, for the α and β hTSH subunits. The anti-β anti-idiotype inhibited l25I-hTSH binding to the β subunit-specific monoclonal quantitatively, whereas 125I-hTSH binding to the α subunit-specific monoclonal was not inhibited by anti-α anti-idiotypes, suggesting that only the former is an “internal image” anti-idiotype. Neither of the two anti-idiotypes nor equimolar mixtures thereof inhibited 125I-bTSH binding to thyroid membranes, even though radiolabelled anti-idiotypes showed saturable binding to thyroid plasma membrane which was inhibited 41-65% by bTSH. Each anti-idiotype alone caused 9% inhibition (compared to 50% by NRIgG) of thyroid plasma membrane adenylate cyclase. Equimolar mixtures (125 μg/ml IgG of each anti-idiotype) induced enzyme activity equivalent to 85% of that of 250 mU/ml of TSH. The TSH-like action of the two anti-idiotypes was also reflected in their capacity to increase (450% by 250 μg/ml IgG compared to normal rabbit IgG) the uptake of 131I into isolated thyrocytes and to promote the organization of such cells into follicular structures. At 250 μg/ml, anti-β anti-idiotype promoted the organization of small follicles and only at a concentration of 500 μg/ml did it enhance 131I uptake. Anti α idiotype was without effect in both assays. Lastly, mixture of anti-idiotypes bound to the ∼ 197,000 Mr band (TSH holoreceptor) on protein blots of thyroid plasma membranes resolved on NaDSO4-polyacrylamide gel electrophoresis under non-reducing conditions. Individual anti-idiotypes were without effect.The TSH α and β subunits apparently deliver two cooperative signals to the receptor and that specificity is associated with the β subunit, while the α subunit is important in enhancing receptor affinity for the heterodimer and in stablizing TSH-receptor complex.
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  • 7
    Electronic Resource
    Electronic Resource
    New York, N.Y. : Wiley-Blackwell
    Journal of Cellular Biochemistry 19 (1982), S. 305-313 
    ISSN: 0730-2312
    Keywords: anti-iodiotypic antibody ; thyrotropin ; receptor ; thyroid stimulating antibody ; Graves disease ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: We raised an antihuman thyrotropin anti-idiotypic antibody and showed that it was active at the thyrotropin receptor. Thus this antibody inhibited 125I b-TSH binding to thyroid plasma membranes, stimulated adenylate cyclase activity through a guanyl nucleotide-dependent mechanism, increased radioiodide entry rate into isolated porcine thyroid follicular cells, and induced such cultured cells to organize into follicles. All these parameters are typical of thyrotropin action. This work raises the possibility that thyroid stimulating antibodies that cause the hyperthyroidism of Graves disease may be, at least in some patients, anti-thyrotropin anti-idiotypic antibodies. It also offers a novel method whereby antireceptor antibodies used in the isolation and characterization of the receptor may be raised from ligands.
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  • 8
    ISSN: 0730-2312
    Keywords: Hashimoto's thyroiditis ; Graves' disease ; microsomal antigen ; TSH receptor ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Antimicrosomal antibodies are present in the sera of most patients with autoimmune thyroiditis, and Graves' disease. It has, in general, been difficult to separate antimicrosomal activity from that directed against the thyrotropin (TSH) receptor in Graves' IgG preparations. The “microsomal” antigen has been localized to the endoplasmic reticulum and microfollicular aspect of thyrocytes; its structure is however unknown. In an attempt to identify the thyroid microsomal antigen, we studied the interaction of Hashimoto's IgG with high microsomal antibody titre and negative for thyroglobulin with purified thyroid plasma and light microsomal membranes. We allowed Hashimoto's, Graves', and control IgGs to bind to protein blots of thyroid plasma membranes resolved on SDS-PAGE under nonreducing conditions. All seven Hashimoto's IgG at a concentration of 2 mg/ml interacted with an M ∼ 197,000 polypeptide corresponding to the TSH holoreceptor. By contrast to Graves' IgG (which were positive at 1 mg/ml), however, this binding was not blocked by pretreatment of the protein blots with TSH. Normal IgGs showed no binding at concentrations of up to 2 mg/ml.Both Hashimoto's and Graves' IgG interacted with TSH-affinity column-purified receptor preparations.Two of the Hashimoto's IgGs induced adenylate cyclase activation in thyroid plasma membranes, three inhibited TSH-stimulated enzyme activation, and two were without effect. Two classes of autoantibodies, other than TSH receptor directed, were encountered; one class raised to antigens common to all seven patients and another class unique to individual patients, eg, Mr 210,000 and Mr 20,000 polypeptides.We propose that the TSH receptor has multiple epitopes (functional domains), and the one to which antimicrosomal antibody bind is likely to be spatially separated from that with which Graves' IgG and TSH interact. Differences in affinity or number of sites allows for the demonstration of Graves' IgG against a background of antimicrosomal antibody.
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  • 9
    ISSN: 0730-2312
    Keywords: internal pH ; transformation ; c-fos ; AP-1 ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Changes in intracellular pH (pHin) take part in the mitogenic response. Their importance has been stressed by the finding that mouse fibroblasts expressing a yeast proton pumping ATPase (PMA1) exhibit a transformed phenotype and are tumorigenic. These cells do maintain a higher pHin, supporting the idea that elevated pHin may act as a proliferative trigger. Here we show that cells constitutively expressing PMA1 have higher levels of the AP-1 transcription factor. The use of stable transfectants and transient transfection assays show that PMA1 activity induces transactivation of the c-fos promoter. The activation of the promoter is mediated throughout the serum response element (SRE). The use of protein kinase C inhibitors suggests that AP-1 activation is achieved through a pathway independent of protein kinase C.
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  • 10
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The role of intracellular pH (pHin) in the regulation of cell growth in both normal and transformed cells is a topic of considerable controversy. In an effort to study this relationship NIH 3T3 cells were stably transfected with the gene for the yeast H+-ATPase, constitutively elevating their pHin. The resulting cell line, RN1a, has a transformed phenotype: The cells are serum independent for growth, clone in soft agar, and form tumors in nude mice. In the present study, we further characterize this system in order to understand how transfection with this proton pump leads to serum-independent growth, using defined media to investigate the effects of specific growth factors on the transfected and parental NIH 3T3 cells. While both cell lines show similar growth increases in response to platelet-derived growth factor (PDGF)-BB and epidermal growth factor (EGF), they respond differently to insulin, insulin-like growth factor-I (IGF-I) and PDGF-AA. RN1a cells exhibit increased growth at nanomolar concentrations of insulin but the parental cells had only a relatively minor response to insulin at 10 μM. Both cell lines showed some response to IGF-I in the nanomolar range but the response of RN1a cells was much larger. Differences in insulin and IGF-I receptor number alone could not explain these results. The two cell lines also respond differently to PDGF-AA. RN1a cells are relatively insensitive to stimulation by PDGF-AA and express fewer PDGF α receptors as shown by Northern blots and receptor-binding studies. We propose a unifying hypothesis in which the H+-ATPase activates a downstream element in the PDGF-AA signal transduction pathway that complements insulin and IGF-I signals, while leading to downregulation of the PDGF α receptor. © 1994 wiley-Liss, Inc.
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