PubMed Health⌕ Search

Biomedical subjects

R Jund

Publications and source records attributed to R Jund.

At least 37 records · Page 2Linked to original sources
PubMed1991

Membrane insertion of uracil permease, a polytopic yeast plasma membrane protein.

Uracil permease is a multispanning protein of the Saccharomyces cerevisiae plasma membrane which is encoded by the FUR4 gene and produced in limited amounts. It has a long N-terminal hydrophilic segment, which is followed by 10 to 12 putative transmembrane segments, and a hydrophilic C terminus. The protein carries seven potential N-linked glycosylation sites, three of which are in its N-terminal segment. Overexpression of this permease and specific antibodies were used to show that uracil permease undergoes neither N-linked glycosylation nor proteolytic processing. Uracil permease N-terminal segments of increasing lengths were fused to a reporter glycoprotein, acid phosphatase. The in vitro and in vivo fates of the resulting hybrid proteins were analyzed to identify the first signal anchor sequence of the permease and demonstrate the cytosolic orientation of its N-terminal hydrophilic sequence. In vivo insertion of the hybrid protein bearing the first signal anchor sequence of uracil permease into the endoplasmic reticulum membrane was severely blocked in sec61 and sec62 translocation mutants.

Blotting, Western↗
PubMed1991

Glucose availability and sensitivity to anoxia of isolated rat peroneal nerve.

The contrast between resistance to ischemia and ischemic lesions in peripheral nerves of diabetic patients was explored by in vitro experiments. Isolated and desheathed rat peroneal nerves were incubated in the following solutions with different glucose availability: 1) 25 mM glucose, 2) 2.5 mM glucose, and 3) 2.5 mM glucose plus 10 mM 2-deoxy-D-glucose. Additionally, the buffering power of all of these solutions was modified. Compound nerve action potential (CNAP), extracellular pH, and extracellular potassium activity (aKe) were measured simultaneously before, during, and after a period of 30 min of anoxia. An increase in glucose availability led to a slower decline in CNAP and to a smaller rise in aKe during anoxia. This resistance to anoxia was accompanied by an enhanced extracellular acidosis. Postanoxic recovery of CNAP was always complete in 25 mM HCO3(-)-buffered solutions. In 5 mM HCO3- and in HCO3(-)-free solutions, however, nerves incubated in 25 mM glucose did not recover functionally after anoxia, whereas nerves bathed in solutions 2 or 3 showed a complete restitution of CNAP. We conclude that high glucose availability and low PO2 in the combination with decreased buffering power and/or inhibition of HCO3(-)-dependent pH regulation mechanisms may damage peripheral mammalian nerves due to a pronounced intracellular acidosis.

Action Potentials↗
PubMed1991

[Spastic movement disorders: non-medicamentous therapies based on neurophysiologic principles].

Lesions of the upper motor neurons cause a spastic syndrome and a central paresis. The consequence of these "plus" and "minus" symptoms on locomotor function is a spastic movement disorder. Strategies of physical therapy for the spastic movement disorders are discussed in relation to research findings in neurophysiology and muscle physiology. The main therapeutic technics are physiotherapy, functional electrical stimulation (FES) and biofeedback training (BFB). Various methodological problems which arise in carrying out and evaluating therapeutic studies are described. Valid prognostic criteria are essential in order to achieve an optimal use of the different therapeutic procedures. This review underlines the need for further research, since some important questions remain open.

Biofeedback, Psychology↗
PubMed1990

The FUR1 gene of Saccharomyces cerevisiae: cloning, structure and expression of wild-type and mutant alleles.

The FUR1 gene of Saccharomyces cerevisiae encodes uracil phosphoribosyltransferase (UPRTase) which catalyses the conversion of uracil into uridine 5'-monophosphate (UMP) in the pyrimidine salvage pathway. The FUR1 gene is included in a 2.1 kb genomic segment of DNA and is transcribed into a 1 kb poly(A)+mRNA. Sequencing has determined a 753 bp open reading frame capable of encoding a protein of 251 amino acids. The FUR1 genes for three recessive fur1 alleles, having different sensibilities to 5-fluorouridine (5-FUR) but identical levels of resistance to 5-fluorouracil (5-FU), were cloned and sequenced. Single bp changes located in different regions of the gene were found in each mutant. Two in vitro-constructed deletions of the FUR1 gene have been integrated at the chromosomal locus, giving strains with 5-FURR and 5-FURR mutant phenotype. Assays of UPRTase, uridine kinase, uridine ribohydrolase and uridine 5'-monophosphate nucleotidase enzymatic activities, in extracts of strains where the FUR1 gene is overexpressed or deleted, indicate that the FUR1 encoded protein possesses only UPRTase activity.

Alleles↗
PubMed1990

The purine-cytosine permease gene of Saccharomyces cerevisiae: primary structure and deduced protein sequence of the FCY2 gene product.

A 2.1 kb DNA segment carrying the purine-cytosine permease gene (FCY2) of Saccharomyces cerevisiae was sequenced, the primary structure of the protein (533 amino acids) deduced and a folding pattern in the membrane is proposed for the permease protein. Expression of the FCY2 gene product requires a functional secretory pathway and is reduced in mnn9, a mutant strain deficient in outer chain glycosylation. The FCY2 gene was mapped on the right arm of chromosome V close to the HIS1 gene.

Amino Acid Sequence↗
PubMed1988

Primary structure of the uracil transport protein of Saccharomyces cerevisiae.

We present in this paper the nucleotidic sequence of the FUR4 gene encoding the uracil permease in the yeast Saccharomyces cerevisiae. The deduced amino acid sequence of the permease has 633 residues; it consists of many hydrophobic stretches, only the N-terminal and C-terminal ends of the protein (about 100 and 50 amino acids respectively) being mostly hydrophilic. No N-terminal hydrophobic signal peptide is present, although it is shown in this work that the biosynthesis of the uracil permease goes through the secretion/glycosylation pathway. Using the results of three different methods, allowing the prediction of transmembrane alpha helices in proteic sequences, we drew a model of folding of the permease in the membrane.

Amino Acid Sequence↗
PubMed1988

Evolutionary relationship and secondary structure predictions in four transport proteins of Saccharomyces cerevisiae.

The comparison of the amino acid sequences of four yeast transport proteins indicates that there is a questionable relatedness between the uracil permease (FUR4) and the purine-cytosine permease (FCY2), whereas the arginine permease (CAN1) and the histidine permease (HIP1) clearly originated from a common molecular ancestor. The analysis of the primary structure of these transport proteins by two methods of secondary structure predictions suggests the presence of 9-12 membrane-spanning alpha-helices in each polypeptide chain. These results are concordant in that 90% of the alpha-helices were determined by both methods to be at the same positions. In the aligned sequences HIP1 and CAN1, the postulated membrane-spanning alpha-helices often start at corresponding sites, even though the overall sequence similarity of the two proteins is only 30%. In the aligned DNA coding sequences of CAN1 and HIP1, synonymous nucleotide substitutions occur with very similar frequencies in regions where the replacement substitution (changing the amino acids) frequencies are widely different. Moreover, our data suggest that the replacement substitutions can be considered as neutral in the N-terminal segment, whereas the other regions are subject to a conservative selective pressure because, if compared to a random drift, the replacement substitutions are underrepresented.

Amino Acid Sequence↗
PubMed1986

Chromosomal mapping of the uracil permease gene of Saccharomyces cerevisiae.

The gene FUR4, coding for the uracil permease in Saccharomyces cerevisiae, was mapped on chromosome II, at a distance of 7.8 cM from the centromere on the right arm of the chromosome. In a first step, we used the chromosome loss mapping method developed by Falco and Botstein (1983) to determine on which chromosome the gene mapped. After the observation that FUR4 was closely linked to GAL10, one of the three genes forming the gal cluster (Bassel and Mortimer 1971), we could determine precisely the position of the gene on chromosome II.

Chromosome Mapping↗
PubMed1981

Expression of a cloned Saccharomyces cerevisiae gene (URA1) is controlled by a bacterial promoter in E. coli and by a yeast promoter in S. cerevisiae.

The expression of a cloned yeast URA1 gene in Escherichia coli and in Saccharomyces cerevisiae was studied. In E. coli, only one orientation of the cloned yeast DNA segment inserted into the bacterial vector (pBR322) allows URA1 expression. Moreover, the permissive orientation changes with the cloning site. The absence of URA1 expression in E. coli can be corrected by the spontaneous integration into the cloned yeast DNA of a 0.9-kb bacterial DNA. Several copies of such a bacterial IS element have been detected in the host E. coli genome. The results strongly suggest that, in E. coli, transcription of the yeast URA1 needs a prokaryotic promoter for its initiation. In S. cerevisiae, the expression of non-chromosomally cloned URA1 does not depend on the orientation of the cloned fragment. Furthermore, it remains under the control of a nuclear regulatory gene (pprX-1) which constitutively enhances the expression of URA1 as well as URA3 at the transcriptional level. Therefore, in S. cerevisiae, transcription of non-chromosomally cloned URA1 involves a physiological yeast promoter cloned along with the structural part of the gene.

Cloning, Molecular↗
PubMed1978

Properties of three distinct pyrimide transport systems in yeast. Evidence for distinct energy coupling.

In Saccharomyces cerevisiae the uptake of cytosine, uracil and uridine is mediated by three permeases. Using mutants blocked in the metabolic utilization of these three compounds we were able to study their specific uptake. Cytosine and uridine show simple saturation kinetics, whereas uracil uptake is a biphasic process. A comparison of the effects of several inhibitors of energy metabolism on these uptake systems was made. Striking differences were found. 2,4-Dinitrophenol (10(-3) M) and NaN3 (10(-2) M) inhibit the entry of the three compounds to similar extent, but chlorhexidine (10(-5) M) and Dio 9 (50 microgram/ml) which are ATPase inhibitors in vitro strongly impaired cytosine and uridine entry and remained without effect on uracil uptake. We provisionally conclude that these systems may be energized by different mechanisms. In the case of cytosine and uridine permease, a membrane ATPase is possibly involved in the process of energetic coupling whereas this does not seem to be so for uracil.

Adenosine Triphosphatases↗
PubMed1977

Evidence for a high proportion of inactive ribosomes in slow-growing yeast cells.

From the protein and RNA content of Saccharomyces cerevisiae growing in different media we calculate that ribosome efficiency is changed: incorporation of amino acids into protein decreases from 8.8 amino acids/s per ribosome in fast-growing cells (0.54 doubling/h) to 5.2 amino acids/s per ribosome in slow-growing cells (0.30 doubling/h). We could not detect significant protein turnover in either fast-or slow-growing cultures, so the lower ribosome efficiency does not seem to be an artifact caused by changes in unstable protein production at different growth rates. Nor is the lower ribosome efficiency due to slower migration of ribosomes along mRNA: the times required to complete polypeptides of known molecular weights are the same in slow-growing cells as those previously determined for fast-growing cells [Waldron, Jund & Lacroute (1974) FEBS Lett. 46, 11-16]. We therefore deduce that ribosome efficiency changes in yeast because the fraction of ribosomes engaged in protein synthesis falls (from 84% in fast-growing cells to 50% in slow-growing cells.

Culture Media↗
PubMed1975

Characterization of cytosine permeation in Saccharomyces cerevisiae.

Cytosine permeation in Saccharomyces cerevisiae has been studied. Cytosine uptake is mediated by a permease which is also responsible for purines transport. The Km for the transport of various substrates of this permease have been determined. By means of appropriate selective techniques, mutants with altered Km and mutants lacking the permease have been selected. Cytosine transport is active and is inhibited by 2,4-dinitrophenol, an uncoupler of oxidative phosphorylation, and by N-ethylmaleimide, a reagent of--SH group. Internal labeled cytosine is chased by addition of unlabeled cytosine in the medium. These results support the hypothesis of a carrier-mediated transport, with reduced internal affinity, allowing the release and accumulation of cytosine in the inner compartment. The efflux of cytosine from cytosine permease-less cells has also been studied and shows first order kinetics. A diffusion coefficient of 5.7 per 10- minus 8 cm per S- minus 1 has been evaluated for this efflux.

Adenine↗
PubMed1972

Regulation of orotidylic acid pyrophosphorylase in Saccharomyces cerevisiae.

Yeast mutants deficient in orotidine-5'-phosphate (OMP) pyrophosphorylase activity have been obtained. The gene encoding this enzyme is unlinked to the four pyrimidine genes previously described. The specific activity of OMP pyrophosphorylase remains constant under all of the physiological conditions used to repress, to derepress, or to induce pyrimidine biosynthesis. This enzyme appears, therefore, to escape the scheme of regulation by mixed repression and induction controlling the other enzymes of the pyrimidine pathway.

Amidohydrolases↗