bluuebunny/crossref_metadata_2025 huggingface dataset:
Presumptive common precursor for neuronal and glial cell lineages in mouse hypothalamus.
Authors: De Vitry F , Picart R , Jacque C , Legault L , Dupouey P , Tixier-Vidal A
Published: May 2006

The cellular localization of a neuronal and a glial cell specific protein (14-3-2 and S-100, respectively) has been explored in mouse hypothalamus in order to trace cell lineages. This study was performed on fixed slices, at the light microscope level, by using either the indirect peroxidase-labeled immunoglobulin technique or immunofluorescence. In the adult, only S-100 immunoreactivity was found in the ependymal layer. In contrast, the magnocellular neurons of the preoptic area displayed strong 14-3-2 immunoreactivity. At neonatal stages (fetal day 17-postnatal day 3), both 14-3-2 and S-100 immunoreactivities developed simultaneously in the same cells lining the ventral part of the third ventricle. Transient detachment of some of these ventricular cells could be visualized before migration in the hypothalamus where they remained as bipotential cells up to postnatal day 10. Later in the development, they differentiated into separate cells, one type containing 14-3-2 and the other S-100, like neurons and glial cells. These results argue for a developmental stage during which cells lining the ventricle are bipotential and may thus be candidates for the role of stem cells for both neuronal and glial lineages.
Somatic cell genetics of adenosine deaminase expression and severe combined immunodeficiency disease in humans.
Authors: Koch G , Shows T B
Published: May 2006

The somatic cell hybrid method has been used to study the number and different types of human genes involved in the expression of adenosine deaminase (ADA; adenosine aminohydrolase, EC 3.5.4.4) in normal cells and cells from a patient with ADA-deficient severe combined immunodeficiency disease (SCID). Genetic and biochemical characterization of ADA in SCID and the ADA tissue-specific isozymes in normal human cells indicates that additional genes, besides the ADA structural gene on chromosome 20, are involved in ADA expression. Human chromosome 6 encodes a gene, ADCP-1, whose presence is necessary for the expression of an ADA-complexing protein in human-mouse somatic cell hybrids [Koch, G. & Shows, T. B. (1978) Proc. Natl. Acad. Sci. USA 75, 3876-3880]. We report the identification of a second gene, ADCP-2, on human chromosome 2, that is also involved in the expression of the ADA-complexing protein. The data indicate that these two ADCP genes must be present in the same cell for that cell to express the complexing protein. Human-mouse somatic cell hybrids, in which the human parental cells were fibroblastss from an individual with ADA-deficient SCID, also required human chromosomes 2 and 6 to express the ADA-complexing protein, indicating that neither ADCP-1 nor ADCP-2 is involved in the ADA deficiency in SCID. The SCID-mouse hybrid cells expressed no human ADA even when human chromosome 20 had been retained. The deficiency of human ADA in these hybrids maps to human chromosome 20, and therefore is not due to the repression or inhibiton of ADA or its product by unlinked genes or gene products. We propose that the expression of the polymeric ADA tissue isozymes in human cells requires at least three genes: ADA on chromosome 20, ADCP-1 on chromosome 6, and ADCP-2 on chromosome 2. A genetic scheme is presented and the different genes involved in ADA expression and their possible functions are discussed.
Isolation of Chinese hamster cell mutants deficient in dihydrofolate reductase activity.
Authors: Urlaub G , Chasin L A
Published: May 2006

Mutants of Chinese hamster ovary cells lacking dihydrofolate reductase (tetrahydrofolate dehydrogenase, 7,8-dihydrofolate:NADP+ oxidoreductase; EC 1.5.1.3) activity were isolated after mutagenesis and exposure to high-specific-activity [3H]deoxyuridine as a selective agent. Fully deficient mutants could not be isolated starting with wild-type cells, but could readily be selected from a putative heterozygote that contains half of the wild-type level of dihydrofolate reductase activity. The heterozygote itself was selected from wild-type cells by using [3H]deoxyuridine together with methotrexate to reduce intracellular dihydrofolate reductase activity. Fully deficient mutants require glycine, a purine, and thymidine for growth; this phenotype is recessive to wild type in cell hybrids. Revertants have been isolated, one of which produces a heat-labile dihydrofolate reductase activity. These mutants may be useful for metabolic studies relating to cancer chemotherapy and for fine-structure genetic mapping of mutations by using available molecular probes for this gene.
Electrophysiology of T lymphocyte cholinergic receptors.
Authors: Shapiro H M , Strom T B
Published: May 2006

The presence of functional muscarinic-cholinergic receptors on at least some T lymphocytes is suggested by the existence of saturable, high-affinity, specific muscarinic binding in T cell-enriched, but not in B cell-enriched, cell suspensions and by observed cholinergic effects on lymphocytes, (e.g., increased lytic capacity of cytotoxic lymphocytes preincubated with muscarinic agents). In this study, we used flow cytometry and a fluorescent probe of membrane potential, the cyanine dye 3,3'-dihexyloxacarbocyanine iodide, to examine the effects of cholinergic agonists and antagonists on the membrane potentials of lymphocytes in T cell-enriched and B cell-enriched suspensions. Acetylcholine (AcCho) and carbamoylcholine (CbmCho) depolarized the membranes of T cells, but not of B cells; the maximal depolarization was produced by 10 nM AcCho or by 1 nM CbmCho. Depolarization following exposure to these concentrations of agonists was maximal by 5-8 min; T cell membrane potentials returned to control values by 13-15 min. Less marked depolarization was produced by 100 nM AcCho and 10 nM CbmCho; 100 pM CbmCho was only slightly less effective than 1 nM CbmCho, and the depolarization persisted 12 min after exposure. Depolarization induced by 1 nM AcCho was abolished when AcCho was combined with 10 nM atropine but not when AcCho was combined with 1 nM atropine or 200 nM d-tubocurarine. The time course of the membrane potential response and its dependence on the relative concentrations of AcCho and specific cholinergic blocking agents correlate well with both binding studies and biological effects. Our results provide evidence that T lymphocytes have functional muscarinic receptors; the flow cytometric method should be generally applicable to studies of the electrophysiology and pharmacology of receptor-ligand interactions.
Hormone-receptor interactions are noncooperative: application to the beta-adrenergic receptor.
Authors: Pollet R J , Standaert M L , Haase B A
Published: May 2006

We have developed kinetic methods with which we have demonstrated that the negatively cooperative hormone-binding model is untenable for the insulin receptor system. These methods have led others to the same conclusion for the thyrotropin and nerve growth factor receptors. We report here the application of these methods to the study of (l)-[propyl-2,3-3H]dihydroalprenolol [(l)-[3H]DHA] binding at 15 degrees C to the beta-adrenergic receptor of the frog erythrocyte--the remaining and most extensively characterized hormone receptor-cyclase system in which negatively cooperative site-site interactions have been reported. Scatchard analysis of the equilibrium binding data for (l)-[3H]DHA in this system is linear. In addition, increasing concentrations of (l)-[3H]DHA during the binding reactions resulted in increasing receptor occupancy but no enhancement of the subsequent dilution-induced dissociation of bound hormone, demonstrating directly that the dissociation rate is independent of occupancy. Furthermore, analysis of the time course of the approach-to-equilibrium for this system at different hormone concentrations was consistent with reversible hormone binding to a homogeneous class of noncooperative receptors, and the analysis yielded a kinetically estimated equilibrium constant consistent with that derived from the linear equilibrium data. The above data indicate that negatively cooperative site-site interactions are not a significant factor for the beta-adrenergic receptor of the frog erythrocyte. These results complete the demonstration that for all known hormone receptor systems, the hormone binds noncooperatively to one or more classes of independent receptor sites. The need for critical reinterpretation of detailed thermodynamic, clinical, and hormone analogue studies based on the negative cooperativity model is discussed.
Neuroendocrine regulation of corpus allatum activity in
Manduca sexta
: Sequential neurohormonal and nervous inhibition in the last-instar larva
Authors: Bhaskaran Govindan , Jones Grace , Jones Davy
Published: May 2006

The inactivation of corpora allata (CA) in the last-instar larva of the tobacco hornworm
Manduca sexta
was studied using
in vivo
assay methods that test the capacity of the glands to induce an extra larval molt. Results indicate that the CA are inactivated by a two-step process. In the first step, a neurohormonal inhibition occurs by day 1 after ecdysis, resulting in a decrease in the ability of the glands to respond to allatotropin. The inhibitory hormone appears to be secreted by the medial neurosecretory cells in the brain and remains in the hemolymph only for a short period of <2 days. The second step of inactivation occurs by day 3; it is neurally mediated and essentially terminates juvenile hormone secretion. Neither the neurohormonal nor the neural inhibition is reversible under the conditions used in our larval assays. The timing of the two stages of inhibition coincides with the two periods of reduction in hemolymph juvenile hormone titer; this suggests that the regulation of corpus allatum activity plays an important role in reducing the juvenile hormone titer during the last larval instar—a prerequisite for the transformation of the larva into the pupa.
gamma-Glutamylamine cyclotransferase: specificity toward epsilon-(L-gamma-glutamyl)-L-lysine and related compounds.
Authors: Fink M L , Chung S I , Folk J E
Published: May 2006

gamma-Glutamylamine cyclotransferase, an enzyme that catalyzes the conversion of L-gamma-glutamylamines to free amines and 5-oxo-L-proline, was found in rabbit kidney and in various other tissues. The specificity of this enzyme indicates that it functions in the metabolism of products of transglutaminase action; among its substrates are epsilon-(L-gamma-glutamyl)-L-lysine, a derivative of this peptide in which the alpha-amino and carboxyl groups of the lysine moiety are blocked, and L-gamma-glutamyl-polyamine derivatives.
Reactivity of reverse transcriptase toward (s4U,U)n copolymers and spin-labeled nucleic acid lattices.
Authors: Warwick P E , Hakam A , Bobst E V , Bobst A M
Published: May 2006

Spin-labeled copolymers of 4-thiouridine and uridine (ls4U,U)n] that contain various amounts of spin label (l) were synthesized by either (i) chemical alkylation of the 4-thiouridine-uridine copolymers (s4U,U)n prepared by copolymerizing 4-thiouridine 5'-diphosphate (s4UDP) and UDP or (ii) copolymerization of spin-labeled s4UDP with UDP using polynucleotide phosphorylase. The effect of (s4U,U)n and (ls4U,U)n on avian myeloblastosis virus (AMV) RNA-dependent DNA polymerase (RNA-dependent DNA nucleotidyltransferase, EC 2.7.7.7; reverse transcriptase) was studied to determine whether the presence of potentially reactive thiol groups or spin labels enhances the inhibitory properties of the copolymers as compared to (U)n. Inhibition by (s4U,U)n gradually increases as the percentage of thiolation increases. Enhanced inhibition by (s4U,U)n appears to be due to the interaction of the thiol groups of (s4U,U)n with the thiol group(s) of the polymerase, because inhibition by (s4U,U)n (8% thiolated) in the presence of dithiotreitol resembles that by (U)n. In contrast, inhibition by (ls4U,U)n containing 3% spin label resembles that by (U)n; however, increasing the spin label to 6% or 12% results in enhanced inhibition by (ls4U,U)n as compared to that by (U)n, and dithiothreitol has no effect on enhanced inhibition by (ls4U,U)n. These results suggest that the mechanism of inhibition observed with (ls4U,U)n with a ls4U:U ratio > 1:33 differs from the mechanism for (s4U,U)n and involves complex formation between the spin label and the essential Zn2+ of RNA-dependent DNA polymerase.
Solubilization of active opiate receptors.
Authors: Simonds W F , Koski G , Streaty R A , Hjelmeland L M , Klee W A
Published: May 2006

Receptors that reversibly bind opiates and opioid peptides have been solubilized from brain and neuroblastoma-glioma hybrid cell NG108-15 membranes. Active receptors are specifically solubilized with a new type of detergent 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate, which is a zwitterionic derivative of cholic acid. The solubilized receptor complexes behave as large molecules with a Stokes radius of 70 A and contain protein as an essential constituent.
Juvenile hormone-binding protein from the cytosol of
Drosophila
Kc cells
Authors: Chang Ernest S. , Coudron Thomas A. , Bruce Marilyn J. , Sage Becky A. , O'Connor John D. , Law John H.
Published: May 2006

Insect cells of an established line,
Drosophila
Kc cells, take up and metabolize juvenile hormone (JH). The cytoplasm of these cells contains a protein that binds JH with specificity, saturability, and high affinity (
K
d
= 1.56 × 10
-8
M). The kinetics for the specific binding and dissociation of JH I were independently measured, and the rate constants were found to be
k
a
= 1.3 × 10
6
M
-1
min
-1
,
k
d
= 1.3 × 10
-2
min
-1
, respectively. All three juvenile hormones bind to the protein with comparable affinities; the corresponding acid or diol metabolites of JH I are not bound. About 2500 hormone-binding protein molecules are present per cell. The protein has a molecular weight of 80,000 as estimated by gel permeation chromatography and by sucrose gradient sedimentation. The properties of this protein suggest that it functions as a cytoplasmic receptor for juvenile hormone.
Polycistronic vesicular stomatitis virus RNA transcripts.
Authors: Herman R C , Schubert M , Keene J D , Lazzarini R A
Published: May 2006

A procedure to enrich for the sequences present at the junction between the linked messages in the polycistronic RNAs symthesized in vitro by vesicular stomatitis virus (VSV) is described. Analyses of these sequences show that they contain a precise transcript of both the intercistronic dinucleotide and the pentanucleotide 5'--C-U-G-U-U--3', common to the 5'-end of all VSV cistrons, covalently linked to the 3'-side of the intervening poly(A). The data strongly suggest that the VSV transcriptase polyadenylylates the mRNAs and can then resume direct and precise transcription of the genome-without reinitiation and without skipping nucleotides.
Iminobiotin affinity columns and their application to retrieval of streptavidin.
Authors: Hofmann K , Wood S W , Brinton C C , Montibeller J A , Finn F M
Published: May 2006

A method is described for the retrieval of streptavidin from the culture broth of Streptomyces avidinii. The key step in this procedure is the adsorption of streptavidin from culture concentrates to an affinity column in which iminobiotin is attached to AH-Sepharose 4B. This column binds streptavbidin at pH 11 and releases the protein at pH 4. The recovery of streptavidin is practically quantitative. The pH dependence of the iminobiotin-avidin affinity, discovered by Green [Green, N. M. (1966) Biochem. J. 101, 774-779], has thus found practical application. The streptavidin bound 4.07 +/- 0.02 mol of [14C]biotin per mol and was essentially homogeneous as judged by disc and slab gel electrophoresis. Streptavidin was extensively succinoylated without loss of biotin-binding capacity. The observations that 125I-labeled streptavidin and 125I-labeled succinoylstreptavidin are retained by iminobiotin-AH-Sepharose 4B columns at pH 7.5 and are eluted at pH 4.0 provides a convenient purification method for these iodinated proteins. The technique employed for the retrieval of streptavidin is generally applicable to the isolation of iminobiotinylated molecules.
Procoat, the precursor of M13 coat protein, requires an electrochemical potential for membrane insertion.
Authors: Date T , Goodman J M , Wickner W T
Published: May 2006

The coat protein of coliphage M13 spans the host cell cytoplasmic membrane prior to its assembly into extruding virus. It is made as a soluble cytoplasmic precursor, termed "procoat," with 23 extra amino acid residues at the NH2 terminus. Procoat binds to the cell membrane and is converted proteolytically to coat protein. When the electrochemical gradient of an infected cell is rapidly dissipated by uncouplers, procoat still binds to the plasma membrane but is not converted to coat. We report here that membrane-bound procoat is only detected at the inner face of the cytoplasmic membrane and that uncouplers prevent it from integrating into a transmembrane conformation.
Activation of brain tryptophan hydroxylase by ATP-MG2+: dependence on calmodulin.
Authors: Kuhn D M , O'Callaghan J P , Juskevich J , Lovenberg W
Published: May 2006

Tryptophan hydroxylase [tryptophan 5-monooxygenase, L-tryptophan,tetrahydropterin:oxygen oxidoreductase (5-hydroxylating), EC 1.14.16.4] is activated by phosphorylating conditions (ATP-Mg2+) in a calcium-dependent, cyclic AMP-independent manner. Addition to the phosphorylation reaction of certain antipsychotic drugs that bind to calmodulin, the heat-stable calcium-binding protein, prevents the activation of tryptophan hydroxylase by ATP-Mg2+ in a concentration-dependent fashion. External addition of purified calmodulin protects the enzyme from the drug-induced effects. Calmodulin-free tryptophan hydroxylase prepared by affinity chromatography on fluphenazine-Sepharose is not activated by ATP-Mg2+ whereas addition of calmodulin to calmodulin-free enzyme restores the responsiveness of the hydroxylase to ATP-MG2+ only in the presence of Ca2+. These results indicate that the activation of tryptophan hydroxylase by phosphorylating conditions is dependent on both calcium and calmodulin.
Surface charge changes in purple membranes and the photoreaction cycle of bacteriorhodopsin.
Authors: Carmeli C , Quintanilha A T , Packer L
Published: May 2006

The surface potential of purple membrane fragments, determined from the distribution of the aqueous free and the membrane-bound positively charged, paramagnetic, amphiphilic probe 4-(dodecyldimethylammonium)-1-oxyl-2,2,6,6-tetramethylpiperidine bromide varied almost 60 mV as a function of ionic strength and 50 mV as a function of pH of the medium. Light-induced changes in surface potential followed the changes observed in the M412 intermediate of the photocycle of bacteriorhodopsin as a function of pH, temperature, and response to antibiotics beauvericin and valinomycin. The number of induced charges per M412 appearing at the surface of purple membranes decreased from about 0.75 to 0.45 as the surface potential became more negative. The stoichiometry would be twice as large if the charge changes were localized exclusively on one side of the purple membrane. Laser flash-induced kinetics of the rise and decay of surface charge changes were slightly slower than the kinetics of the rise and decay of M412 which is associated with the reversible deprotonation of the retinal Schiff base nitrogen in the chromophore. It is suggested that the light-induced charge changes monitor a dissociable amino acid residue which may be a step in the movement of protons across the purple membrane.
Evolution of recombination in a constant environment
Authors: Feldman Marcus W. , Christiansen Freddy B. , Brooks Lisa D.
Published: May 2006

The theory of evolution at a selectively neutral locus that controls the recombination between two major loci that are under selection is studied. If the major loci are at a stable equilibrium in linkage disequilibrium under selection and recombination, then a mutation at the modifier locus will increase in frequency when rare if and only if it decreases the recombination fraction. If the major loci are in disequilibrium at a balance between selection against deleterious alleles and mutation towards them, then two new phenomena are observed. First, a recombination increasing mutation will succeed if the disequilibrium is negative and the modifier is sufficiently tightly linked to the major loci. Second, depending on the strength of selection, even if the disequilibrium is negative, recombination reduction may occur for looser linkage between the major and modifier loci.
Cotransfer of circular and linear prokaryotic and eukaryotic DNA sequences into mouse cells.
Authors: Hsiung N , Warrick H , deRiel J K , Tuan D , Forget B G , Skoultchi A , Kucherlapati R
Published: May 2006

We have attempted to introduce some eukaryotic and prokaryotic DNA sequences into mouse fibroblasts. Purified herpes thymidine kinase gene (tk) was introduced into mouse cells. The presence of the herpes tk gene was established by gel electrophoresis, sensitivity to the purine analog acyloguanosine, and Southern blot hybridization. We utilized two different methods to introduce nonselectable markers into mouse cells. Bacterial plasmid pBR322 was ligated to herpes tk and used for transfection. All cells that were TK+ also contained the plasmid sequences. In the second method, pBR322 DNA was mixed with herpes tk DNA and presented to mouse cells. TK+ cells were tested for pBR322 sequences by blot hydridization. The frequency of unlinked cotransfer was greater than 40%. When the circular plasmid containing pBR322 and tk was used for transfection, each of the resulting transfectants acquired several copies of the plasmid. Most of the copies were associated with high molecular weight DNA in the cell. In addition, we found that some of the plasmid molecules may exist as free circular molecules. Using the nonligated cotransfer method, we introduced purified human beta-globin sequences into the recipient cells. We were unable to detect any transcripts of the human beta-globin gene at a level greater than or equal to 10 molecules per cell.
DNA-transformed murine teratocarcinoma cells: regulation of expression of simian virus 40 tumor antigen in stem versus differentiated cells.
Authors: Linnenbach A , Huebner K , Croce C M
Published: May 2006

Thymidine kinase-deficient (TK-; ATP:thymidine 5'-phosphotransferase, EC 2.7.1.21)F9 teratocarcinoma stem cells have been transformed with a recombinant plasmid genome consisting of the pBR322 genome linked to a herpes simplex virus type 1 thymidine kinase gene (HSV-1 tk) and a simian virus 40 (SV40) genome. A clonal line of stem cells was obtained that contains only one copy of plasmid DNA, which is integrated into murine chromosomal DNA through a site on the pBRR322 genome. The HSV-1 tk gene, which is adjacent to the SV40 genome, is expressed in stem cells, whereas SV40 gene expression is not detectable. If differentiation of these stem cells is induced, the differentiated cells express SV40 early gene products. Thus, we have constructed a stem cell which contains a set of genes (SV40), the expression of which is regulated differently in stem and differentiated cells. This cell line could be used to determine the mechanism of suppression of expression of these genes in stem cells.
Liver tumors distinguished by immunofluorescence microscopy with antibodies to proteins of intermediate-sized filaments.
Authors: Bannasch P , Zerban H , Schmid E , Franke W W
Published: May 2006

Antibodies against constitutive proteins of different types of intermediate-sized filaments were used in immunofluorescence microscopy on frozen sections of normal rat liver and various rat liver tumors induced by treatment with nitrosamines. Antibodies to tonofilament prekeratin stained bile duct epithelia and hepatocytes of normal liver and hepatocellular carcinoma cells and ductal cells of cholangiofibromas. These cells were not significantly stained by antibodies to vimentin. By contrast, antibodies to vimentin stained mesenchymal cells of normal liver and cells of early and advanced angiosarcomas and of undifferentiated spindle cell sarcoma. These mesenchymal tumor cells were not stained with antibodies to prekeratin. The presence of intermediate-sized filaments in these tumors, often in large whorl-like aggregates, was also demonstrated by electron microscopy. The results show that immunofluorescence microscopy with antibodies to cytoskeletal proteins is a powerful tool for the classification and differential diagnosis of mesenchymal and epithelial liver tumors. We propose that staining with antibodies to proteins of different types of intermediate filaments can be used to improve the identification of tumors of other organs, including metastases, as well as non-neoplastic proliferative lesions.
Radiometric analysis of biological oxidations in man: sex differences in estradiol metabolism.
Authors: Fishman J , Bradlow H L , Schneider J , Anderson K E , Kappas A
Published: May 2006

The oxidative metabolism of estradiol was studied in normal men and women by a radiometric procedure that provides information on the totality of the biotransformations concerned. The release of 3H into body water from estradiol labeled with 3H in the 17 alpha, 16 alpha, and C-2 positions permits measurement of the rate and extent of 17 beta-ol oxidation and of the competing hydroxylations at C-2 and 16 alpha, which lead to products with different biologicaly properties. In both men and women the 17 beta-ol oxidation is the most rapid transformation, followed by 2-hydroxylation and finally by 16 alpha-hydroxylation. Hydroxylation at C-2 predominates by a faccto of 2-4 over 16 alpha-hydroxylation. In men a large fraction (37%) of the substrate is unmetabolized at any of the three sites and is not excreted in urine; in women the corresponding fraction is only 18%. The estradiol fraction that does undergo metabolism is hydroxylated at C-2 vs. 16 alpha to a greater extent in women than in men. These major sex differences in the metabolism of estradiol in the human may have an important influence on the expression of the biological actions of the hormone. The radiometric technique used in this study can be generally applied to study the oxidative transformations of hormones, drugs, and other exogenous chemical that can be specifically labeled at reactive sites.
Activation of membrane-bound kallikrein and renin in the kidney.
Authors: Nishimura K , Alhenc-Gelas F , White A , Erdös E G
Published: May 2006

Rat kidney contains membrane-bound renin (EC 3.4.99.19) and kallikrein (EC 3.4.21.8). Kallikrein activity was measured by a spectrophotometric assay and renin by radioimmunoassay. Plasma membrane-bound kallikrein was activated by lysolecithin and by melittin, which was a more potent activator., This activation by mellitin was independent of calcium concentration. Mellitin was, however, a more potent activator of membrane-bound renin in the presence of calcium. Administration of aldosterone to rats for 6 days increased kallikrein activity in the renal homogenate and in the membrane-enriched fractions, whereas renin activity was not affected. It was proposed that kallikrein may also be located on the basal membrane of tubular epithelial cells, where aldosterone can enhance its activity.
Bäcklund transformations and nonlinear differential difference equations
Authors: Levi D. , Benguria R.
Published: May 2006

It is shown that any Bäcklund transformation of a nonlinear differential equation integrable by the multichannel Schrödinger eigenvalue problem can be written in the form

V
x

=
U′V
-
VU
. This allows us to interpret the Bäcklund transformation formally as a nonlinear differential difference equation for which we can immediately construct the soliton solutions.
A theoretical study of resonance Raman scattering from molecules: High pressure effect
Authors: Fujimura Y. , Lin S. H. , Eyring H.
Published: May 2006

The main purpose of this paper has been to study the high pressure effect on the resonance Raman scattering (RRS) of molecules in a dense medium. In deriving the RRS cross section under high pressure, a different approach from that presented in the previous papers has been used, and the resulting expression for the RRS cross section can be used to treat both pressure and temperature effects.
Human plasma fibrinogen heterogeneity: evidence for an extended carboxyl-terminal sequence in a normal gamma chain variant (gamma').
Authors: Wolfenstein-Todel C , Mosesson M W
Published: May 2006

Two types of normal human plasma fibrinogen--peak 1 and peak 2--are distinquishable by DEAE-cellulose gradient elution chromatography. The elution characteristics of peak 2 fibrinogen, which amounts to about 15% of the total, are attributable to the presence of a gamma chain variant, gamma', which is more negatively charged than gamma chains and makes up about half of all such chains in that peak [Mosesson M. W., Finlayson, J. S. & Umfleet, R. A. (1972), J. Biol. Chem. 247, 5223-5227]. Analyses of reduced S-carboxymethylated fibrin that had first been incubated in the presence of Factor XIIIa plus the fluorescent amine donor dansylcadaverine (DNScad) showed that the same amount of this compound could be incorporated covalently into either type of gamma chain. Furthermore, the DNScad-labeled COOH-terminal CNBr fragment (CNBr e) derived from the S-carboxymethylated gamma chain was smaller than the DNScad-labeled fragment (CNBr e') from the gamma' chain (Mr, 3200 and 4900) by about the same amount as the difference in size between the respective parent chains (Mr, 49,400 and 51,500). DNScad-CNBr e or DNScad-cNBR e' could be further cleaved by trypsin to yield a smaller fluorescent fragment corresponding to the penultimate tryptic gamma chain peptide containing the DNScad-glutamine acceptor and lysine donor crosslinking functions. The COOH-terminal amino acids of gamma and gamma' chains were valine and leucine, respectively. The rates of Factor XIIIa-catalyzed crosslinking of peak 1 and peak 2 fibrin were the same, but peak 1 fibrin gamma chains formed only one species of crosslinked dimer (gamma gamma) whereas peak 2 fibrin gamma chains yielded three (gamma gamma, gamma gamma', gamma'gamma'). We conclude that gamma' chains are functionally normal but have an extended COOH-terminal sequence accounting for their more negative charge and larger size relative to gamma chains.
Genetic structure of avian myeloblastosis virus, released from transformed myeloblasts as a defective virus particle
Authors: Duesberg Peter H. , Bister Klaus , Moscovici Carlo
Published: May 2006

Chicken myeloblasts transformed by avian myeloblastosis virus (AMV) in the absence of nondefective helper virus (termed nonproducer cells) were found to release a defective virus particle (DVP) that contains avian tumor viral
gag
proteins but lacks envelope glycoprotein and a DNA polymerase. Nonproducer cells contain a Pr76
gag
precursor protein and also a protein that is indistinguishable from the Pr180
gag-pol
protein of nondefective viruses. The RNA of the DVP is 7.5 kilobases (kb) long and is 0.7 kb shorter than the 8.2-kb RNAs of the helper viruses of AMV, MAV-1 and MAV-2. Comparisons based on RNA·cDNA hybridization and mapping of RNase T1-resistant oligonucleotides indicated that DVP RNA shares with MAV RNAs nearly isogenic 5′-terminal
gag
and
pol
-related sequences of 5.3 kb and a 3′-terminal c-region of 0.7 kb that is different from that found in other avian tumor viruses. Adjacent to the c-region, DVP RNA contains a contiguous specific sequence of 1.5 kb defined by 14 specific oligonucleotides. Except for two of these oligonucleotides that map at its 5′ end, this sequence is unrelated to any sequences of nondefective avian tumor viruses of four different envelope subgroups as well as to the specific sequences of fibroblast-transforming avian acute leukemia and sarcoma viruses of four different RNA subgroups. The specific sequence of the DVP RNA is present in infectious stocks of AMV from this and other laboratories in an AMV-transformed myeloblast line from another laboratory, and it is about 70% related to nucleotide sequences of E26 virus, an independent isolate of an AMV-like virus. Preliminary experiments show DVP to be leukemogenic if fused into susceptible cells in the presence of helper virus. We conclude that DVP RNA is the leukemogenic component of infectious AMV and that its specific sequence, termed
AMV
, may carry genetic information for oncogenicity. Thus we have found here a transformation-specific RNA sequence, unrelated to helper virus, in a highly oncogenic virus that does not transform fibroblasts.
Processing of the precursor to corticotropin and beta-lipotropin in humans.
Authors: Miller W L , Johnson L K , Baxter J D , Roberts J L
Published: May 2006

The biosynthesis of human corticotropin (ACTH) was studied in organ culture of pituitary adenomas and by translating mRNA from an ectopic ACTH-producing tumor in a cell-free system. Peptides similar to human ACTH, beta-lipotropin, and the amino-terminal glycopeptide are cleaved from a common precursor with an apparent molecular weight of 35,000 on sodium dodecyl sulfate/polyacrylamide gels. The precursors synthesized in pituitary and ectopic ACTH-producing tissues are indistinguishable. The cleavage sites of the peptide chain appear to be similar to those previously deduced for murine and bovine ACTH. Immunoprecipitation studies suggest that the primary structure of the precursor peptide is similar in all three species. However, glycosylation is different in the human and murine precursors: the precursor to human ACTH appears to be glycosylated only in the amino-terminal fragment, not in the ACTH or beta-lipotropin sequences. Studies with an autopsied normal human pituitary suggest that neither normal nor adenomatous pituitary tissue glycosylates the ACTH sequence.
Ligand-linked phase changes in a biological system: applications to sickle cell hemoglobin.
Authors: Wyman J , Gill S J
Published: May 2006

Polyphasic linkage is a close analog of the allosteric and polysteric linkages shown by many biological macromolecules. Like them, it gives rise to both homotropic and heterotropic effects. It is governed by a group of linkage potentials applicable to each separate phase and also, subject to certain conditions, by a group of lower order applicable to the whole system, globally. A good example of polyphasic linkage is provided by sickle cell hemoglobin which, under suitable conditions and subject to control by oxygen, precipitates out of solution to form what appear to be microtubules. This is but one instance of the way in which macromolecular assembly and the formation of subcellular structures generally can be regulated by various small molecules acting as ligands.
The energy relay: a proofreading scheme based on dynamic cooperativity and lacking all characteristic symptoms of kinetic proofreading in DNA replication and protein synthesis.
Authors: Hopfield J J
Published: May 2006

A mechanism for proofreading biosynthetic processes requiring high accuracy is described. The previously understood "kinetic proofreading" mechanism of enhancing accuracy has distinguishing characteristics such as the non-stoichiometric use of substrate or cosubstrate that have allowed its identification in aspects of DNA and protein synthesis. The proofreading scheme developed here, though generically related, lacks all the previous identifying features. A DNA polymerase proofreading in this manner need neither generate dNMP nor have a 3' leads to 5' exonuclease activity. Protein synthesis could be proofread even with stoichiometric GTP consumption or without elongation factor Tu . GTP. The kinetic scheme that generates this proofreading makes use of an "energy relay" from previous substrate molecules and is a representative of a class of nonequilibrium processes displaying dynamic cooperativity. This proofreading mechanism has its own identifying characteristics, which are sufficiently subtle that they would have generally escaped notice or defied interpretation.
Cloning of an origin of DNA replication of Xenopus laevis.
Authors: Watanabe S , Taylor J H
Published: May 2006

DNA fragments of Xenopus laevis, the African frog, were cloned in the EcoRI site of the Escherichia coli plasmid pACYC189 and tested for ability to initiate and complete replication of the recombinant plasmid when injected into unfertilized eggs of X. laevis. After measurement of the [3H]-thymidine incorporation per egg for a number of recombinant plasmids, pSW14 and pSW9, which respectively contain a small segment (550 base pairs) and several kilobases of frog DNA, were selected for more extensive analysis. In spite of the small size of the segment in pSW14, it incorporates in 2 hr at least 3 times as much labeled thymidine as either pSW9 or the vector alone. The DNA synthesis in pSW14 was shown to be replication rather than repair synthesis, based on a buoyant density shift of the product when iododeoxyuridine was used for labeling. To determine the number of replications of pSW14, a novel method was employed. Because pSW14 is a head-to-head dimer of the vector with the Xenopus fragment inserted at an EcoRI site, the plasmid has three methylatable sites--two bracketing the Xenopus fragment and one opposite the fragment. By cotransformation of E. coli with pSW14 and pBR322 containing the EcoRI methylase gene, supercoiled pSW14 was methylated and injected into eggs with [3H]thymidine. Disappearance of modified EcoRI sites by semiconservative replication was followed by measuring the sensitivity to EcoRI endonuclease over time. The results showed that about 50% of the labeled, supercoiled DNA recovered from eggs after 4 hr was sensitive to EcoRI digestion, which indicates that most of the DNA that incorporated [3H]thymidine had replicated twice during the 4 hr in the unfertilized eggs of X. laevis. We conclude that pSW14 has a functional origin in the Xenopus DNA segment.
Specific inhibition of renin by an angiotensinogen analog: studies in sodium depletion and renin-dependent hypertension.
Authors: Burton J , Cody R J , Herd J A , Haber E
Published: May 2006

The angiotensin substrate analog Pro-His-Pro-Phe-His-Phe-Phe-Val-Tyr-Lys has no significant effect on blood pressure in sodium-replete monkeys (Macaca fascicularis) but blocks the pressor response to infused human renin. Pressor responses to angiotensin I and angiotensin II are not attenuated. In five studies in sodium-depleted monkeys, an infusion of 2 mg of the peptide per kg of body weight resulted in a reduction of mean arterial pressure (MAP) from 105 +/- 4 to 79 +/- 3 mm Hg, which is not significantly different from the response to 1 mg of the angiotensin I-converting enzyme inhibitor teprotide per kg. In uninephrectomized monkeys, inflation of a suprarenal aortic cuff caused an increase in MAP from 107 +/- 3 to 131 +/- 3 mm Hg. Infusion of 0.6 mg of the renin-inhibitory peptide per kg was followed by a return of blood pressure to 107 +/- 4 mm Hg--a depressor response similar to that observed with teprotide. This specific in vivo inhibitor of renin can now be applied to a wide variety of physiologic studies.
Complex of simian virus 40 large tumor antigen and 48,000-dalton host tumor antigen.
Authors: Greenspan D S , Carroll R B
Published: May 2006

Simian virus 40 large tumor antigen (T Ag) can be separated by sucrose gradient sedimentation into a rapidly sedimenting, maximally phosphorylated fraction and a slowly sedimenting, less phosphorylated fraction. The Mr 48,000 host tumor antigen (48,000 HTA, also called nonviral T Ag) is preferentially complexed with the maximally phosphorylated T Ag. Pulse-labeled T Ag sediments as a 5-6S monomer, whereas T Ag radiolabeled for progressively longer periods slowly increases in sedimentation coefficient to give a broad distribution between 5 S and greater than 28 S. Mutation in the viral A locus causes a decrease in T Ag phosphorylation and a marked decrease in 48,000 HTA binding, shifting the sedimentation coefficient of T Ag to the monomer value. The more highly phosphorylated T Ag also has the highest affinity for chromatin.
Prophage (phi 80) induction in Escherichia coli K-12 by specific deoxyoligonucleotides.
Authors: Irbe R M , Morin L M , Oishi M
Published: May 2006

A cell preparation that is permeable to proteins and oligonucleotides yet produces infectious phage particles after induction treatments was obtained by plasmolysis of Escherichia coli cells lysogenic for phi 80. When the permeabilized cells were exposed to specific oligo(deoxynucleotides), prophage (phi 80) was induced during further incubation. Of the dinucleotides tested, only d(A-G), d(G-G), and d(I-G) induced prophage. The essential base sequence of the deoxydinucleotides for the induction was determined to be deoxy(purine-G). Among oligo(deoxynucleotides) with unique base composition examined, only oligo(deoxyguanylates) exhibited the inducing activity. Although this specific oligo(deoxynucleotide)-triggered induction occurred in recB- cells, the induction was not detected in recA- cells or in the cells lysogenic for induction-negative phi 80(ind-). Possible biological significance of the oligo(deoxynucleotide)-triggered prophage induction is discussed.
DNase I hypersensitive sites in Drosophila chromatin occur at the 5' ends of regions of transcription.
Authors: Keene M A , Corces V , Lowenhaupt K , Elgin S C
Published: May 2006

By using a map of the unique region of DNA encoding the fur small heat-shock proteins of Drosophila melanogaster (hsp 22, hsp 23, hsp 26, and hsp 28), and a simple mapping technique, the positions of the DNase I hypersensitive sites of chromatin in the vicinity of these genes have now been determined. The major chromatin-specific sites occur at the 5' ends of each of the four heat-shock protein genes in embryo nuclei. These genes are not active in the nuclei analyzed but can be quickly induced in these cells by the heat-shock stimulus. The chromatin structure indicated by DNase I hypersensitivity may be a necessary factor in the general mechanism of gene activation.
Ring contraction of hydroporphinoid to corrinoid complexes
Authors: Rasetti Vittorio , Pfaltz Andreas , Kratky Christoph , Eschenmoser Albert
Published: May 2006

Crystalline nickel(II) and dicyanocobalt(III) complexes of a racemic 1,2,2,7,7,12,12,17,17,20-decamethyl-20-hydroxy-1,2,3,7,8,12,13,20-octahydro- 17
H
-porphyrin rearrange to the corresponding complexes of racemic 19-acetyl-1,2,2,7,7,12,12,17,17-nonamethyl-
trans
-corrin on melting (approximately 290°C and 260°C, respectively). The nickel(II) 19-acetylcorrinate formed in this way is shown to deacetylate to racemic nickel(II) 1,2,2,7,7,12,12,17,17-nonamethyl-
trans
-corrinate on treatment with 2 M KOH. These reactions are being studied as potentially biomimetic chemical models for the elusive ring contraction step in vitamin B
12
biosynthesis.
Phytochrome induces photoreversible calcium fluxes in a purified mitochondrial fraction from oats
Authors: Roux Stanley J. , McEntire Kerry , Slocum Robert D. , Cedel Thomas E. , Hale Calvin C.
Published: May 2006

Previous studies have indicated that phytochrome regulates Ca
2+
fluxes across the plasma membrane of plant cells. In this study we investigated whether phytochrome can also regulate such fluxes across mitochondrial membranes, using the Ca
2+
-sensitive dye murexide to monitor the uptake and release of Ca
2+
by mitochondria. The results showed that Ca
2+
fluxes in these organelles could be photoreversibly altered, red light diminishing the net uptake rate and far-red light restoring this rate to its dark control level. Treatment of the mitochondria with ruthenium red blocked their Ca
2+
uptake. In the presence of this inhibitor, red light induced a net efflux of Ca
2+
from the mitochondria, and subsequent far-red light reduced this efflux to nearly zero, the dark control level. Light-induced rate changes in Ca
2+
flux, both with and without the inhibitor, persisted for several minutes in the dark and remained photoreversible through several irradiations for as long as 30 min. The purity of the mitochondrial preparation was judged to be about 80% by electron microscopic morphometry; most of the phytochrome present was localized on the mitochondria in the preparation by using immunocytochemical methods. Taken together with previous findings, the results suggest that red light activation of phytochrome would initiate an increase in the cytosolic Ca
2+
concentration. The results are integrated with the fact that calmodulin is a component of plant cell cytoplasms to construct a model postulating that phytochrome directs photomorphogenesis in part through its regulation of Ca
2+
and calmodulin-controlled enzyme activities.
Interactions of calmodulin with coated vesicles from brain.
Authors: Linden C D , Dedman J R , Chafouleas J G , Means A R , Roth T F
Published: May 2006

Coated vesicles purified in the presence of calcium are enriched approximately 7-fold in calmodulin content relative to standard preparations isolated in the absence of free calcium. Radioiodinated calmodulin binds specifically to coated vesicles in vitro. Binding is saturable (Kd, 10 nM) and calcium dependent. Half-maximal binding occurs at 2.4 microM free Ca2+ whereas up to 1.2 mM Mg2+ has no effect on binding. Troponin C, a protein homologous to calmodulin, competes with binding of 125I-labeled calmodulin with 1/30th the affinity of native calmodulin. Chromatography of 2 M urea-solubilized coated vesicles on a calmodulin-Sepharose column demonstrated a Ca2+-dependent interaction of coated vesicle proteins and calmodulin. The properties of calmodulin binding to coated vesicles are comparable to those of calmodulin activities in other systems.
On the dynamics of the Ising model of cooperative phenomena
Authors: Montroll Elliott W.
Published: May 2006

A two-dimensional (and to some degree three-dimensional) version of Glauber's one-dimensional spin relaxation model is described. The model is constructed to yield the Ising model of cooperative phenomena at equilibrium. A complete hierarchy of differential equations for multispin correlation functions is constructed. Some remarks are made concerning the solution of them for the initial value problem of determining the relaxation of an initial set of spin distributions.
Linkage of the four gamma subclass heavy chain genes.
Authors: Roeder W , Maki R , Traunecker A , Tonegawa S
Published: May 2006

The genes for the heavy-chain constant regions of the four gamma subclass immunoglobulins were identified in a set of overlapping mouse DNA fragments representing about 100 kilobase pairs (kb) of the mouse genome that was cloned from bacteriophage lambda libraries of BALB/c mouse embryo DNA. R-loop mapping studies show that the genes are located 5'-C gamma 3-34 kb-C gamma 1-21 kb-C gamma 2b-15 kb-C gamma 2a-3' and lie in the same transcriptional orientation. Two DNA segments, one of 19 kb and another of 15 kb, that surround the C gamma 2b and C gamma 2a genes, respectively, show considerable homology and implicate a tandem duplication mechanism in the evolution of this gene cluster.