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)

Sucrose transport from the apoplasm, across the plasma membrane, and into the symplast is critical for growth and development in most plant species. Phloem loading, the process of transporting sucrose against a concentration gradient into the phloem, is an essential first step in long-distance transport of sucrose and carbon partitioning. We report here that a soybean 62-kD sucrose binding protein is associated with the plasma membrane of several cell types engaged in sucrose transport, including the mesophyll cells of young sink leaves, the companion cells of mature phloem, and the cells of the developing cotyledons. Furthermore, the temporal expression of the gene and the accumulation pattern of the protein closely parallel the rate of sucrose uptake in the cotyledon. Molecular cloning and sequence analysis of a full-length cDNA for this 62-kD sucrose binding protein indicated that the protein is not an invertase, contains a 29-amino acid leader peptide that is absent from the mature protein, and is not an integral membrane protein. We conclude that the 62-kD sucrose binding protein is involved in sucrose transport, but is not performing this function independently.
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PMID:A 62-kD sucrose binding protein is expressed and localized in tissues actively engaged in sucrose transport. 146 54

It has been shown previously that defects in the essential GTP-binding protein, Ypt1p, lead to a block in protein transport from the endoplasmic reticulum (ER) to the Golgi apparatus in the yeast Saccharomyces cerevisiae. Here we report that four newly discovered suppressors of YPT1 deletion (SLY1-20, SLY2, SLY12, and SLY41) to a varying degree restore ER-to-Golgi transport defects in cells lacking Ypt1p. These suppressors also partially complement the sec21-1 and sec22-3 mutants which lead to a defect early in the secretory pathway. Sly1p-depleted cells, as well as a conditional lethal sly2 null mutant at nonpermissive temperatures, accumulate ER membranes and core-glycosylated invertase and carboxypeptidase Y. The sly2 null mutant under restrictive conditions (37 degrees C) can be rescued by the multicopy suppressor SLY12 and the single-copy suppressor SLY1-20, indicating that these three SLY genes functionally interact. Sly2p is shown to be an integral membrane protein.
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PMID:The yeast SLY gene products, suppressors of defects in the essential GTP-binding Ypt1 protein, may act in endoplasmic reticulum-to-Golgi transport. 144 80

We have produced the four subunits of the nicotinic acetylcholine receptor of Torpedo californica, an integral membrane protein, in the yeast Saccharomyces cerevisiae. Two of the subunits (alpha and delta) were readily produced from their cDNAs after simply subcloning them into a yeast shuttle vector adjacent to a yeast promoter. The other two protein subunits (beta and gamma) were not produced by this strategy, although the amounts of mRNA produced from these expression constructs are similar to those for alpha and delta. Replacing the DNA coding for the normal N-terminal signal sequences for the beta and gamma subunits with DNA coding for the signal sequence of yeast invertase results in successful protein synthesis. The yeast signal sequence allows these subunits to be translocated across the membrane of the endoplasmic reticulum and to be glycosylated. The appropriate final size of the subunit proteins suggests that the yeast signal sequence has been properly cleaved after translocation.
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PMID:Expression of Torpedo nicotinic acetylcholine receptor subunits in yeast is enhanced by use of yeast signal sequences. 218 89

The Neurospora plasma membrane H(+)-ATPase is a polytopic integral membrane protein. To localize transmembrane segments, mutants were constructed that contained the amino and carboxyl termini of the H(+)-ATPase with putative transmembrane segment. A stretch of amino acid residues from yeast invertase that has three consensus N-linked glycosylation sites was placed carboxyl terminal of the putative transmembrane segment. RNA transcripts of these mutants were translated in a Neurospora in vitro system that was supplemented with microsomes from Neurospora. By the criteria of glycosylation of the polypeptide chain, resistance to extraction at pH 11.5, and protection from proteinase K digestion, only one transmembrane segment could be identified within the amino acid residues 272-314 of the primary sequence of the H(+)-ATPase.
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PMID:Topology of the Neurospora plasma membrane H(+)-ATPase. Localization of a transmembrane segment. 810 34

To analyze the mechanism of integral membrane protein localization in the early Golgi apparatus of Saccharomyces cerevisiae, we have used Och1p, a cis-Golgi mannosyltransferase. A series of influenza virus hemagglutinin (HA) epitope-tagged fusion proteins was constructed in which invertase is appended to the Golgi-luminal carboxy terminus of full-length Och1p. Several constructs included a Kex2p cleavage site between the Och1p and invertase moieties to monitor transit to the Kex2p-containing TGN. Cells expressing an Och1p-invertase fusion do not secrete invertase, but those expressing an Och1p-Kex2p site-invertase fusion protein secrete high levels of invertase in a Kex2p-dependent manner. The Och1p-Kex2p site-invertase fusion protein is cleaved with a half-time of 5 min, and the process proceeds to completion. Before cleavage the protein receives glycosyl modifications indicative of passage through the medial- and trans-Golgi, therefore cleavage occurs after ordered anterograde transport through the Golgi to the TGN. Transit to distal compartments is not induced by the invertase moiety, since noninvertase fusion constructs encounter the same glycosyltransferases and Kex2p as well. The Och1p-HA moiety, irrespective of whether it is generated by cleavage of the fusion protein in the TGN or synthesized de novo, is degraded with a half-time of about 60 min. Thus, the half-time of degradation is 12-fold longer than the time required to reach the TGN. At steady state, de novo-synthesized and TGN-generated HA epitope-tagged Och1p reside in a compartment with a buoyant density identical to that of wild-type Och1p and distinct from that of the vacuole or the TGN. Finally, och1 null cells that express an Ochlp fusion construct known to rapidly encounter the TGN glycosylate invertase to the same extent as wild-type cells, indicating that they have phenotypically wild-type Och1p activity. These results lead us to propose a model for Och1p-HA localization that involves movement to distal compartments, at least as far as the TGN, followed by retrieval to the cis compartment, presumably by vesicular transport.
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PMID:Localization of a yeast early Golgi mannosyltransferase, Och1p, involves retrograde transport. 860 97

Overproduction of an endoplasmic reticulum (ER)-resident membrane protein (cytochrome P450 52A3) and of a secretory protein (invertase) was used to study the regulation of the luminal ER protein Kar2p under conditions that lead to ER proliferation and secretory overload, respectively. In both cases we found (i) a significant increase of Kar2 protein and mRNA levels, (ii) a transcriptional regulation based on the the function of the 22 bp unfolded-protein-response element of the KAR2 promoter and (iii) an essential role of the transmembrane kinase Ire1p for upregulation of KAR2 gene expression. These results show that the same mechanism operates when KAR2 induction is triggered by overproduction of cytochrome P450 or invertase and that this mechanism shares the known features of the unfolded-protein-response pathway. Disruption of the IRE1 gene resulted in a marked decrease of the invertase protein levels produced. In contrast, a functional IRE1 gene was not required to reach high-level production of the integral membrane protein cytochrome P450 52A3, Moreover, IRE1 gene disruption did not prevent P450-induced ER proliferation. We suggest that Ire1p-mediated KAR2 induction is, in the case of cytochrome P450 52A3 overproduction, a process which follows on ER proliferation, thereby monitoring the increase of ER size and adjusting the level of Kar2p accordingly.
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PMID:Inducible membranes in yeast: relation to the unfolded-protein-response pathway. 936 46

The regulation of vesicular transport in eukaryotic cells involves Ras-like GTPases of the Ypt/Rab family. Studies in yeast and mammalian cells indicate that individual family members act in vesicle docking/fusion to specific target membranes. Using the two-hybrid system, we have now identified a 248 amino acid, integral membrane protein, termed Yip1, that specifically binds to the transport GTPases Ypt1p and Ypt31p. Evidence for physical interaction of these GTPases with Yip1p was also demonstrated by affinity chromatography and/or co-immunoprecipitation. Like the two GTPases, Yip1p is essential for yeast cell viability and, according to subcellular fractionation and indirect immunofluorescence, is located to Golgi membranes at steady state. Mutant cells depleted of Yip1p and conditionally lethal yip1 mutants at the non-permissive temperature massively accumulate endoplasmic reticulum membranes and display aberrations in protein secretion and glycosylation of secreted invertase. The results suggests for a role for Yip1p in recruiting the two GTPases to Golgi target membranes in preparation for fusion.
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PMID:Specific binding to a novel and essential Golgi membrane protein (Yip1p) functionally links the transport GTPases Ypt1p and Ypt31p. 972 32

The frizzled (fz) gene is required for development of planar tissue polarity in the epidermis of Drosophila melanogaster; it likely encodes an integral membrane protein that functions as a receptor for a tissue polarity-signaling molecule. On the basis of hydropathy analyses, it has been postulated that Fz protein contains seven transmembrane domains. Consistent with that model, the amino terminus of Fz was found to be extracellular, whereas the carboxyl terminus was intracellular. In the present study, the membrane topology of Fz was further examined in vivo by constructing various fz-suc2 fusion genes and analyzing their invertase activity in transformed yeast. We observed that plating efficiency and growth rate on sucrose media, as well as invertase secretion, were consistent with the proposed seven-pass model of Fz. This study provides the first experimental assessment of overall Fz topology.
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PMID:Frizzled-suc2 fusion gene studies in Saccharomyces cerevisiae. 1036 Aug 43

The general amino acid permease (Gap1p) of Saccharomyces cerevisiae is an integral membrane protein that contains 12 hydrophobic regions predicted to be membrane-spanning segments. A topological reporter construct, encoding an internal 53-amino acid peptide of invertase (Suc2p) containing three Asp-X-Ser/Thr glycosylation sites, was inserted in-frame into the hydrophilic NH(2)- and COOH-terminal domains and each of the 11 hydrophilic loops that separate the 12 hydrophobic segments of Gap1p. The resulting 13 gene sandwich fusion proteins were expressed in a gap1Delta null mutant strain; 9 of these retain amino acid transport activity and are folded and correctly targeted to the plasma membrane. The glycosylation state of each of the fusion proteins was monitored; the results indicate that all 12 hydrophobic segments of Gap1p span the membrane, and the NH(2) and COOH termini are cytoplasmically oriented. These results were independently tested by isolating sealed right-side-out microsomes from sec12-1 strains expressing six different Gap1p constructs containing functional factor Xa protease cleavage sites. The pattern of factor Xa protease cleavage was found to be consistent with the presence of 12 membrane-spanning domains. Gap1p exhibited the same membrane topology in strains lacking Shr3p; therefore, Gap1p fully integrates into the ER membrane independently of this permease-specific packaging chaperone.
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PMID:A method for determining the in vivo topology of yeast polytopic membrane proteins demonstrates that Gap1p fully integrates into the membrane independently of Shr3p. 1090 20