Biomedical subjects

J C Walker

Publications and source records attributed to J C Walker.

At least 55 records · Page 3Linked to original sources

PubMed1995

Plant protein kinase families and signal transduction.

Enzymes of the eukaryotic protein kinase superfamily catalyze the reversible transfer of the gamma-phosphate from ATP to amino acid side chains of proteins. Protein kinase function can be counteracted by the action of phosphoprotein phosphatases. Phosphorylation status of a protein can have profound effects on its activity and interaction with other proteins. An estimated 1 to 3% of functional eukaryotic genes encode protein kinases, suggesting that they are involved in many aspects of cellular regulation and metabolism. In plants, protein phosphorylation has been implicated in responses to many signals, including light, pathogen invasion, hormones, temperature stress, and nutrient deprivation. Activities of several plant metabolic and regulatory enzymes are also controlled by reversible phosphorylation. As might be expected from this diversity of function, there is a large array of different protein kinases. Purification of protein kinases and their subsequent cloning, facilitated by the PCR and advances in homology-based cloning techniques, as well as functional analyses, including complementation of conditional yeast mutants and positional cloning of mutant plant genes, has already led to identification of more than 70 plant protein kinase genes. However, the precise functional roles of specific protein kinases and phosphatases during plant growth and development have been elucidated for only a few.

Amino Acid Sequence↗

PubMed1995

Reconstitution of Arabidopsis casein kinase II from recombinant subunits and phosphorylation of transcription factor GBF1.

In contrast to the well-defined tetrameric structure of animal and yeast casein kinase II (CKII), plant CKII is found in two forms: a monomeric form and an oligomeric form whose subunit composition is not well defined. The Arabidopsis homologs of the catalytic subunit alpha (CKA1) and the regulatory subunit beta (CKB1) of CKII were expressed in Escherichia coli to examine their ability to form complexes, the effect of CKB1 on the catalytic activity, and the relationship of the recombinant enzymes to those isolated from plant material. Both subunits were found mainly in the inclusion body fraction in the bacterial expression strains, and they were solubilized and renatured with the recovery of catalytic (CKA1) and stimulatory (CKB1) activities. The combination of purified CKA1 and CKB1 proteins resulted in up to 100-fold stimulation of casein kinase activity compared with the CKA1 activity alone, showing that CKB1 has biochemical properties similar to those of the beta subunit from animals. CKA1 and CKB1 spontaneously assembled into a tetrameric complex, CKA1(2)CKB12, which had properties very similar to those of the oligomeric CKII form isolated from broccoli. However, the properties of the catalytic subunit CKA1 alone differed from those of the broccoli monomeric form of CKII-like activity. Phosphorylation of transcription factor GBF1 with the reconstituted CKA1(2)CKB1(2) enzyme resulted in stimulation of its DNA binding activity and retardation of the protein-DNA complex; these results are identical to those obtained previously with isolated nuclear CKII from broccoli.

Animals↗

PubMed1995

Climatic forcing of carbon-oxygen isotopic covariance in temperate-region marl lakes.

Carbon and oxygen stable isotopic compositions of lacustrine carbonate from a southeastern Michigan marl lake display linear covariance over a range of 4.0% Peedee belemnite (PDB) in oxygen and 3.9% (PDB) in carbon. Mechanisms of delta 13 C-delta 18 O coupling conventionally attributed to lake closure in arid-region basins are inapplicable to hydrologically open lake systems. Thus, an alternative explanation of isotopic covariance in temperate region dimictic marl lakes is required. We propose that isotopic covariance is a direct record of change in regional climate. In short-residence-time temperate-region lake basins, summer meteoric precipitation is enriched in 18O relative to winter values, and summer organic productivity enriches epilimnic dissolved inorganic carbon in 13C. Thus, climate change toward longer summers and/or shorter winters could result in greater proportions of warm-month meteoric precipitation, longer durations of warm-month productivity, and net long-term enrichment in carbonate 18O and 13C. Isotopic covariance observed in the Michigan marl lake cores is interpreted to reflect postglacial warming from 10 to 3 ka followed by cooler mean annual temperature, a shift toward greater proportions of seasonal summer precipitation, a shortening of the winter season, or some combination of these three factors.

Carbon↗

PubMed1994

Interaction of a protein phosphatase with an Arabidopsis serine-threonine receptor kinase.

A protein phosphatase was cloned that interacts with a serine-threonine receptor-like kinase, RLK5, from Arabidopsis thaliana. The phosphatase, designated KAPP (kinase-associated protein phosphatase), is composed of three domains: an amino-terminal signal anchor, a kinase interaction (KI) domain, and a type 2C protein phosphatase catalytic region. Association of RLK5 with the KI domain is dependent on phosphorylation of RLK5 and can be abolished by dephosphorylation. KAPP may function as a signaling component in a pathway involving RLK5.

Amino Acid Sequence↗

PubMed1994

Biochemical properties of the autophosphorylation of RLK5, a receptor-like protein kinase from Arabidopsis thaliana.

The RLK5 gene of Arabidopsis thaliana encodes a novel receptor-like protein kinase. DNA sequence analysis suggests that the RLK5 protein contains an extracellular domain that has 21 tandemly repeated leucine-rich motifs linked, via a transmembrane hydrophobic region, to a protein kinase catalytic domain that is related to the serine/threonine family of protein kinases. To study the intrinsic biochemical properties of this protein kinase we have expressed the catalytic domain as two different recombinant fusion proteins in Escherichia coli. Both hybrid proteins have similar kinetic properties, autophosphorylate on serine and threonine residues and have significantly greater activity in the presence of Mn2+ than Mg2+. A lysine to glutamic acid substitution in the catalytic domain of RLK5 results in the catalytically inactive protein RLK5(Cat)K711E. The active RLK5 protein can phosphorylate the inactive K711E protein and the K711E protein can partially inhibit the autophosphorylation of RLK5. Tryptic cleavage of the autophosphorylated proteins followed by two-dimensional thin layer electrophoresis indicates that several sites in the catalytic domain are phosphorylated.

Arabidopsis↗

PubMed1994

Effects of odorants and irritants on respiratory behavior.

A technique that combines psychophysical measurements with continuous recording of nasal patency and respiratory behavior was used to study the psychophysical and respiratory responses of 10 subjects to well-controlled stimulation with three compounds differing in relative stimulatory effectiveness for nasal olfactory and trigeminal chemoreceptors. All four concentrations of acetic acid, amyl acetate, and phenethyl alcohol were well above the odor detection threshold. The magnitudes of both the increase in odor strength and nasal irritation and the decreases in tidal volume were greatest for acetic acid and least for phenethyl alcohol. Among the odorants, differences in nasal irritation were greater than those in odor strength, and tidal volume appeared to have a reasonably close and inverse relationship to nasal irritation.

Acetates↗

PubMed1994

Structure and function of the receptor-like protein kinases of higher plants.

Cell surface receptors located in the plasma membrane have a prominent role in the initiation of cellular signalling. Recent evidence strongly suggests that plant cells carry cell surface receptors with intrinsic protein kinase activity. The plant receptor-like protein kinases (RLKs) are structurally related to the polypeptide growth factor receptors of animals which consist of a large extracytoplasmic domain, a single membrane spanning segment and a cytoplasmic domain of the protein kinase gene family. Most of the animal growth factor receptor protein kinases are tyrosine kinases; however, the plant RLKs all appear to be serine/threonine protein kinases. Based on structural similarities in their extracellular domains the RLKs fall into three categories: the S-domain class, related to the self-incompatibility locus glycoproteins of Brassica; the leucine-rich repeat class, containing a tandemly repeated motif that has been found in numerous proteins from a variety of eukaryotes; and a third class that has epidermal growth factor-like repeats. Distinct members of these putative receptors have been found in both monocotyledonous plants such as maize and in members of the dicotyledonous Brassicaceae. The diversity among plant RLKs, reflected in their structural and functional properties, has opened up a broad new area of investigation into cellular signalling in plants with far-reaching implications for the mechanisms by which plant cells perceive and respond to extracellular signals.

Amino Acid Sequence↗

PubMed1994

Isolation of an Arabidopsis thaliana casein kinase II beta subunit by complementation in Saccharomyces cerevisiae.

Casein kinase II is thought to play an essential role in the control of cell division and differentiation in all eukaryotes. Through complementation of a defective casein kinase II catalytic subunit gene from Saccharomyces cerevisiae, we isolated an Arabidopsis thaliana casein kinase II regulatory subunit homologue, CKB1. A second regulatory subunit was identified by low-stringency hybridization with CKB1. Casein kinase II from S. cerevisiae is composed of two catalytic (alpha) and two regulatory (beta) subunits. Simultaneous disruption of the genes for the alpha and alpha' subunits, CKA1 and CKA2, respectively, is lethal. Strain YDH8 has disruptions of CKA1 and CKA2; its viability depends on a temperature-sensitive allele of CKA2, cka2-8, carried on a centromeric plasmid. We screened an A. thaliana cDNA library, whose inserts are under the control of the galactose-inducible GAL10 promoter, for cDNAs which enabled YDH8 cells to grow at the restrictive temperature. One cDNA, CKB1, was isolated by this screen which had homology to cDNAs of casein kinase II beta subunits. A second cDNA, CKB2, was isolated by hybridization and was also able to suppress the YDH8 mutant phenotype. The proteins encoded by CKB1 and CKB2 are 80% identical. The carboxy-terminal two thirds of both proteins is ca. 54% identical to the regulatory beta subunits of casein kinase II from other species. The amino termini are unrelated to any other known proteins. CKB1 and CKB2 lack the conserved autophosphorylation site characteristic of animal beta subunits, but have potential casein kinase II phosphorylation sites in the same region. Suppression of the cka1 delta cka2-8 mutant phenotype occurs by interaction of CKB1 with the defective, cka2-8-encoded, catalytic subunit. Cells with disruptions in CKA1 and CKA2 are not rescued by expression of CKB1.

Amino Acid Sequence↗

PubMed1993

Cloning and sequence of a chicken alpha-N-acetylgalactosaminidase gene.

A cDNA clone encoding the mature polypeptide for the chicken liver alpha-N-acetylgalactosaminidase enzyme was isolated by screening a cDNA library with a synthetic sequence derived from the human alpha-N-acetylgalactosaminidase gene. The deduced amino acid sequence of the chicken liver clone was identical to the amino-terminal and cyanogen bromide derived peptide sequences obtained from the purified enzyme. The chicken enzyme has 75% identity with the human alpha-N-acetylgalactosaminidase and 56-33% identity with alpha-galactosidases from several sources.

Amino Acid Sequence↗

PubMed1993

Molecular cloning of two novel protein kinase genes from Arabidopsis thaliana.

We have isolated two novel protein kinase genes, MHK and NAK, from the plant Arabidopsis thaliana by using low stringency hybridization with the catalytic domain of a putative plant receptor protein kinase. Sequence analysis of the cDNAs reveals that MHK is a member of the cdc2+ family of protein kinases and is particularly similar to the mak gene of rats; mak encodes a protein kinase that may play a role in spermatogenesis. NAK encodes a candidate protein kinase that is similar to the oncogenes met and abl. The homology that these two Arabidopsis genes share with other protein kinases suggests that they may play a role in the regulation of plant growth and development.

Amino Acid Sequence↗

PubMed1993

Parasitology: diagnostic techniques in the laboratory.

Recent advances in diagnostic techniques for parasitic diseases, such as improved serological and molecular techniques, have been accompanied by improvements in the traditional methods involving staining and microscopy. Timing of tests and background information about where the patient has been are important factors. Detailed information is given of the appropriate specimens for diagnosis of protozoan and helminthic infections and of the sensitivity and specificity of the various tests.

Clinical Laboratory Techniques↗

PubMed1993

Expression of multiple type 1 phosphoprotein phosphatases in Arabidopsis thaliana.

Type 1 phosphoprotein Ser/Thr phosphatases (PP1) are highly conserved enzymes found in all eukaryotes. These enzymes have multiple functions in fungal and animal cells but little is known of their function and regulation in plants. Previous studies in our laboratory indicated that maize and Arabidopsis contain a family of PP1 genes and/or pseudogenes. In this study, we report the isolation of five distinct Arabidopsis cDNA clones (TOPP1, TOPP2, TOPP3, TOPP4 and TOPP5) which encode the catalytic subunit (PP1c) of type 1 protein phosphatases. Genomic Southern blot analyses indicate that these clones are the products of five distinct genes and that an additional 2-3 PP1c genes and/or pseudogenes may be present in the Arabidopsis genome. The derived amino acid sequences of the TOPP clones are very similar to published sequences of PP1c from animals, fungi and plants. Four of the TOPP amino acid sequences show unique structural features not observed in other PP1c sequences from fungi or animals. All of the TOPP genes are expressed in Arabidopsis roots, rosettes and flowers, although TOPP1, TOPP2 and TOPP3 appear to be expressed at higher levels in these tissues than TOPP4 and TOPP5.

Amino Acid Sequence↗

PubMed1993

Structure and expression of the S locus-related genes of maize.

The extracellular of the putative receptor-like protein kinase, ZmPK1, is related to the self-incompatibility locus (S-locus) genes of Brassica. We have isolated and characterized a genomic DNA clone of ZmPK1 and three additional genes from maize that are highly related to ZmPK1. These three S-locus related genes do not appear to have the protein kinase catalytic domain that is found in ZmPK1. One or more of these genes are expressed specifically in the silks. This initial description of S-locus related genes in monocotyledonous plants suggests that the S-locus domain may be involved in several different cellular functions in a wide variety of plants.

Base Sequence↗

PubMed1993

Abrupt climate change and transient climates during the Paleogene: a marine perspective.

Detailed investigations of high latitude sequences recently collected by the Ocean Drilling Program (ODP) indicate that periods of rapid climate change often culminated in brief transient climates, with more extreme conditions than subsequent long term climates. Two examples of such events have been identified in the Paleogene; the first in latest Paleocene time in the middle of a warming trend that began several million years earlier: the second in earliest Oligocene time near the end of a Middle Eocene to Late Oligocene global cooling trend. Superimposed on the earlier event was a sudden and extreme warming of both high latitude sea surface and deep ocean waters. Imbedded in the latter transition was an abrupt decline in high latitude temperatures and the brief appearance of a full size continental ice-sheet on Antarctica. In both cases the climate extremes were not stable, lasting for less than a few hundred thousand years, indicating a temporary or transient climate state. Geochemical and sedimentological evidence suggest that both Paleogene climate events were accompanied by reorganizations in ocean circulation, and major perturbations in marine productivity and the global carbon cycle. The Paleocene-Eocene thermal maximum was marked by reduced oceanic turnover and decreases in global delta 13C and in marine productivity, while the Early Oligocene glacial maximum was accompanied by intensification of deep ocean circulation and elevated delta 13C and productivity. It has been suggested that sudden changes in climate and/or ocean circulation might occur as a result of gradual forcing as certain physical thresholds are exceeded. We investigate the possibility that sudden reorganizations in ocean and/or atmosphere circulation during these abrupt transitions generated short-term positive feedbacks that briefly sustained these transient climatic states.

Animals↗

PubMed1993

Receptor-like protein kinase genes of Arabidopsis thaliana.

The isolation of a maize cDNA clone that encodes a membrane spanning protein kinase related to the self-incompatibility glycoproteins (SLG) of Brassica and structurally similar to the growth factor receptor tyrosine kinases has recently been reported. Three distinct receptor-like protein kinase (RLK) cDNA clones from Arabidopsis thaliana have now been identified. Two of the Arabidopsis RLK genes encode SLG-related protein kinases but have different patterns of expression: one is expressed predominantly in rosettes while the other is expressed primarily in roots. The third RLK gene contains an extracellular domain that consists of 21 leucine-rich repeats that are analogous to the leucine-rich repeats found in proteins from humans, flies and yeast. The Arabidopsis leucine-rich gene is expressed at equivalent levels in roots and rosettes. These results show that there are several genes in higher plants that encode members of the receptor protein kinase superfamily. The structural diversity and differential expression of these genes suggest that each plays a distinct and possibly important role in cellular signaling in plants.

Amino Acid Sequence↗

PubMed1992

Possible methane-induced polar warming in the early Eocene.

Reconstructions of early Eocene climate depict a world in which the polar environments support mammals and reptiles, deciduous forests, warm oceans and rare frost conditions. At the same time, tropical sea surface temperatures are interpreted to have been the same as or slightly cooler than present values. The question of how to warm polar regions of Earth without noticeably warming the tropics remains unresolved; increased amounts of greenhouse gases would be expected to warm all latitudes equally. Oceanic heat transport has been postulated as a mechanism for heating high latitudes, but it is difficult to explain the dynamics that would achieve this. Here we consider estimates of Eocene wetland areas and suggest that the flux of methane, an important greenhouse gas, may have been substantially greater during the Eocene than at present. Elevated methane concentrations would have enhanced early Eocene global warming, and also might specifically have prevented severe winter cooling of polar regions because of the potential of atmospheric methane to promote the formation of optically thick, polar stratospheric ice clouds.

Atmosphere↗

PubMed1992

Human ectopic fascioliasis in Australia: first case reports.

OBJECTIVE: To describe the manifestations of two cases of migratory ectopic fascioliasis diagnosed in Australia, including the first report of lymphatic infection. PRESENTATION: Both patients presented with acute, superficial swellings. In the first, a 46-year-old woman, the lump was found to be a cervical lymph node containing a mature Fasciola hepatica which had released eggs into surrounding tissues. The second patient was a 34-year-old male abattoir worker, in whom the subcutaneous lesion resembled an infected sebaceous cyst and contained an immature fluke. FINDINGS: Both lesions were resected and diagnosed histologically. Fasciola eggs were not found in the faeces of either patient. Blood eosinophilia was not detected in either case. A serological test for fascioliasis was carried out in the second case and the result was positive. In both cases, infection was probably acquired in Australia, although neither patient had eaten watercress. OUTCOME: Neither patient was specifically treated with anthelminthic agents, and neither suffered further complications. CONCLUSION: Migratory fascioliasis occurs in Australia. It can present as superficial or deep focal lesions, not necessarily in association with peripheral blood eosinophilia or Fasciola eggs in faeces. Serological tests may be helpful in diagnosing such cases.

Adult↗

PubMed1992

Identification of a maize nucleic acid-binding protein (NBP) belonging to a family of nuclear-encoded chloroplast proteins.

A cDNA encoding a nuclear-encoded chloroplast nucleic acid-binding protein (NBP) has been isolated from maize. Identified as an in vitro DNA-binding activity, NBP belongs to a family of nuclear-encoded chloroplast proteins which share a common domain structure and are thought to be involved in posttranscriptional regulation of chloroplast gene expression. NBP contains an N-terminal chloroplast transit peptide, a highly acidic domain and a pair of ribonucleoprotein consensus sequence domains. NBP is expressed in a light-dependent, organ-specific manner which is consistent with its involvement in chloroplast biogenesis. The relationship of NBP to the other members of this protein family and their possible regulatory functions are discussed.

Amino Acid Sequence↗