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J M Clement

Publications and source records attributed to J M Clement.

16 recordsLinked to original sources
PubMed1999

CTP:phosphocholine cytidylyltransferase: insights into regulatory mechanisms and novel functions.

A key regulatory enzyme in phosphatidylcholine biosynthesis, CTP:cholinephosphate cytidylyltransferase (CCT), catalyzes the formation of CDP-choline. This review discusses the essential features of CCT and addresses intriguing new insights into the catalytic and regulatory properties of this complex enzyme. Characterization of a lipid-binding segment in rat CCT is described and the role of lipids in CCT activation is discussed. An analysis of the phosphorylation domain is presented and possible physiological rationales for reversible phosphorylation of CCT are discussed. The nuclear localization of CCT is examined in the context of multiple CCT isoforms, as is recent evidence establishing a potential link between CCT activity and vesicular transport.

Amino Acid Sequence↗
PubMed1992

Na+/Ca2+ exchange in plasma membrane vesicles from a glucose-responsive insulinoma.

Plasma membrane vesicles from a glucose-responsive insulinoma exhibited properties consistent with the presence of a membrane Na+/Ca2+ exchange. The exchange was rapid, reversible, and was dependent on the external Ca2+ concentration (Km = 4.1 +/- 1.1 microM). External Na+ inhibited the uptake in a dose-dependent manner (IC50 = 15 mM). Dissipation of the Na+ gradient by 10 microM monensin decreased Na+/Ca2+ exchange from 0.74 +/- 0.17 nmoles/mg protein/s to 0.11 +/- 0.05 nmoles/mg protein/s. Exchange was not influenced by veratridine, tetrodotoxin and ouabain, or by modifiers of cAMP. No effect was seen using the calcium channel blockers, nitrendipine or nifedipine. Glucose had no direct effect on Na+/Ca2+ exchange, while glyceraldehyde, glyceraldehyde-3-phosphate and dihydroxyacetone inhibited the exchange. Na+ induced efflux of calcium was seen in Ca2+ loaded vesicles and was half maximal at [Na+] of 11.1 +/- 0.75 mM. Ca2+ efflux was dependent on [Na+], with a Hill coefficient of 2.7 +/- 0.07 indicating that activation of Ca2+ release involves a minimum of three sites. The electrogenicity of this exchange was demonstrated using the lipophilic cation tetraphenylphosphonium [( 3H]-TPP), a membrane potential sensitive probe. [3H]-TPP uptake increased transiently during Na+/Ca2+ exchange indicating that the exchange generated a membrane potential. These results show that Na+/Ca2+ exchange operates in the beta cell and may be an important regulator of intracellular free Ca2+ concentrations.

Animals↗
PubMed1991

Bacterial vectors to target and/or purify polypeptides: their use in immunological studies.

The construction of recombinant proteins by genetic engineering has opened new avenues in basic research (studies on protein organization, protein folding, immunogenicity of proteins, ...) and many different applications. Recombinant proteins which keep properties of both parental proteins are especially interesting. For example, if one protein--the vector protein--is targeted to a given cellular compartment, the other protein--the passenger--may be identically targeted. Also, if the vector protein can be purified by a simple affinity chromatographic procedure, this property may be extended to the passenger. The authors have developed a genetic procedure to detect "permissive" sites within potential vector proteins so that genetic fusion to these sites keep most or all biological properties of the vector. When they used LamB, an outer membrane protein from E. coli, foreign sequences could be expressed at the bacterial cell surface. This may lead to several types of applications: live bacterial vaccines, simple diagnostic tests, selection procedures for peptides with biological activity. When they used the MalE protein, a periplasmic maltose binding protein from E. coli, the passengers could be exported and purified in one-step high affinity chromatography in mild non-denaturing conditions. This led us to a simple preparation and purification scheme for the soluble part of the CD4 receptor for the Human Immunodeficiency Virus (HIV).

Bacterial Outer Membrane Proteins↗
PubMed1989

Direct repeats at nuclear matrix-associated DNA regions and their putative control function in the replicating eukaryotic genome.

Short DNA regions, known to contain replication origins, were isolated from 2 M NaCl resistant nuclear structures of Physarum polycephalum after predigestion with DNase. Regions of 100 bp average length were cloned and sequenced. About 25% of the clones contained direct repeats of 12 to 16 bp and variable base sequences, that have been shown to possess the potential of playing a crucial role in the control of DNA replication. In one of the two alternative three-dimensional configurations such repeats expose single-stranded loops that can function as sites for the initiation of new DNA strands. As these regions are converted into full-length duplexes by their own replication, reinitiation at the same site is excluded. Restoration of the initiationable configuration is considered to be coupled to structural rearrangements involved in the transient condensation of chromosomes in mitosis. This mechanisms ensures that any part of the entire eukaryotic genome is reproduced just a single time during one cell cycle.

Base Sequence↗
PubMed1987

Chromosome studies in IgA-deficient patients.

Chromosome analysis was performed in 17 children with IgA-deficiency. In two patients a constitutional structural chromosome abnormality was found. A ring chromosome 22 was seen in one, while in the other a mosaicism of ring chromosome 18/18p+ was observed. Both patients were mentally retarded and showed distinct congenital defects. From ten asymptomatic patients, spontaneous as well as X-ray-induced chromosome instability was investigated. There was no increased spontaneous instability, and also after irradiation the induced chromosome damage was within normal control levels. A relationship between IgA-deficiency and X-ray hypersensitivity, as might be suggested by the frequently occurring coincidence of radiosensitivity and IgA-deficiency in ataxia telangiectasia patients, is not established.

Adolescent↗
PubMed1986

Palindromic units from E. coli as binding sites for a chromoid-associated protein.

Several hundred copies of a highly conserved extragenic palindromic sequence, 20-40 nucleotides long, exist along the chromosome of E. coli and S. typhimurium. These have been defined as palindromic units (PU) or repetitive extragenic palindromes (REP). No general function for PUs has been identified. In the present work, we provide data showing that a protein associated with a chromoid extract of E. coli protects PU DNA against exonuclease III digestion. This provides the first experimental evidence that PU constitutes binding sites for a chromoid-associated protein. This result supports the hypothesis that PUs could play a role in the structure of the bacterial chromoid.

Bacterial Proteins↗
PubMed1984

Further sequence analysis of the phage lambda receptor site. Possible implications for the organization of the lamB protein in Escherichia coli K12.

We present the DNA sequence alterations due to seven lamB missense mutations yielding resistance to phages lambda and K10. They reveal five different amino acid positions in the LamB protein. Three positions (245, 247 and 249) define a new region required for phage adsorption. The two other positions (148 and 152) belong to a region where mutations to phage resistance has already been detected. These two regions are hydrophilic and could belong to turns of the protein located at the surface of the cell. All the missense mutational alterations to phage resistance sequenced in the LamB protein correspond to 10 sites located in four different segments of the polypeptide chain. We discuss their location in terms of the notion of phage receptor site and of a working model for the organization of this protein in the outer membrane of Escherichia coli.

Amino Acid Sequence↗
PubMed1982

Analysis of lambda receptor and beta-lactamase synthesis and export using cloned genes in a minicell system.

We have cloned lamB, the gene for lambda receptor (an outer membrane protein), on a small plasmid which also carries the gene for beta-lactamase (a periplasmic protein). We have identified a promoter in the region of malK, the gene immediately preceding lamB, which is active in minicells but relatively inactive in vitro. Using a minicell system, we have found that both lambda receptor and beta-lactamase are made as full length precursors which are subsequently processed. We also show that the lambda receptor precursor can be exported to the outer membrane before it is processed. Mature beta-lactamase is found only in the periplasm, suggesting that processing may be a requirement for export to the periplasm.

Bacteriophage lambda↗
PubMed1982

Mutations in gene lamB: studies on structure and topology of an E. coli outer membrane protein.

Results obtained in E. coli with a set of mutations conferring tight resistance to phage lambda lead to a first identification of three residues in the lamB protein which are important for adsorption of phage lambda. Residues 151 and 382 are important for reversible adsorption while residue 401 is important for irreversible adsorption. The identification of such residues may help to identify portions of the protein located at the cell surface. Assays of lambda receptor activity in merodiploid strains heterogenote for gene lamB show that the mutations studied can have a negative dominant effect. For one class of mutations (class II) this can be interpreted by negative complementation at the level of oligomerisation. The data confirm then that active lambda receptor is a trimer.

Amino Acid Sequence↗
PubMed1980

DNA sequence encoding the NH2-terminal peptide involved in transport of lambda receptor, an Escherichia coli secretory protein.

lamB encodes the lambda receptor of Escherichia coli, an outer membrane protein. We have identified the beginning of the lamB gene by correlating DNA nucleotide sequence with a partial sequence of the primary translation product of lamB. We show that lambda receptor is synthesized as a precursor containing an extra 25 amino acids at its NH2 terminus. These amino acids are predominately hydrophobic and probably comprise a structure required for initiation of transport of lambda receptor from the cytoplasm to the outer membrane.

Amino Acid Sequence↗
PubMed1977

Gas-liquid chromatographic determination of butylated hydroxyanisole and butylated hydroxytoluene in edible oils.

A method is described for the quantitative determination of butylated hydroxyanisole and butylated hydroxytoluene in edible oils. Both antioxidants are extracted with acetonitrile, and quantitated by gas-liquid chromatography, using a hydrogen flame ionization detection system and di-tert-butyl-4-hydroxyanisole as an internal standard. The standard addition technique is used. Recoveries from oils containing 70-400 ppm by weight of both antioxidants ranged from 88 to 104%.

Anisoles↗
PubMedDate not supplied

Weaning from mechanical ventilatory support.

Weaning patients from mechanical ventilatory support continues to be a major challenge in critical care units. This article discusses recent research in the area of weaning and identifies specific parameters related to successful weaning in clinical practice.

Clinical Nursing Research↗