bluuebunny/crossref_metadata_2025 huggingface dataset:
Polymorphism of human B-cell alloantigens: evidence for three loci within the HLA system.
Authors: Markert M L , Cresswell P
Published: May 2006

The B-cell alloantigens of an HLA-DR3-homozygous, MB2-homozygous, MT2-positive lymphoblastoid cell line were studied by two-dimensional gel electrophoresis. Analysis of gel patterns suggested assignment of the HLA-DR3 determinant to the larger (35,000-dalton) subunit (alpha) of the B-cell alloantigen. MB2 was found to be either a determinant on the small (27,000 dalton) subunit (beta) or a crossreactive determinant(s) on the HLA-DR3 alpha subunit and an additional alpha subunit. MT2 was found to be a determinant on Ia antigen-like molecules distinct from those carrying the MB and HLA-DR determinants. The results are consistent with the existence in the major histocompatibility complex of at least three loci encoding B-cell alloantigens.
Chronic hepatitis in chimpanzee carriers of hepatitis B virus: morphologic, immunologic, and viral DNA studies.
Authors: Shouval D , Chakraborty P R , Ruiz-Opazo N , Baum S , Spigland I , Muchmore E , Gerber M A , Thung S N , Popper H , Shafritz D A
Published: May 2006

Years after infection with hepatitis B virus, chimpanzees may have manifestations of the carrier state as described in man. In addition to serologic evidence for persistent viral infection, percutaneous liver biopsy specimens showed hepatitis B virus surface antigen in the cytoplasm and hepatitis B virus core antigen in the nucleus. Four carrier animals had portal inflammatory reaction as seen in human chronic persistent hepatitis. Viral DNA was demonstrated in nucleic acid extracts of liver biopsy specimens by molecular hybridization to cloned plasmic pA01 containing hepatitis B virus DNA sequences. Although a viral molecule of length greater than the putative virus was identified, it did not appear to represent integration of viral DNA into the host genome. The chimpanzee model may serve as a means to study the mechanism of hepatitis B viral persistence and progression to chronic liver disease.
Elongating nerve fibers are guided by a pathway of material released from embryonic nonneuronal cells.
Authors: Collins F , Garrett J E
Published: May 2006

Dissociated parasympathetic neurons rapidly initiate neurite outgrowth when exposed to culture medium previously conditioned by the growth of embryonic heart cells. The inducer of neurite outgrowth in the conditioned medium is a substratum-conditioning factor; that is, it does not act in a soluble form, but acts only when bound to the nerve cell culture substratum. When a sharp border is created between a region of the substratum coated with this factor and a region coated with unconditioned medium, neurites fail to cross this border; rather, they change their direction of outgrowth so as to remain on the conditioned substratum. Thus, long after the initiation of outgrowthhas been induced, elongating neurites continue to respond to the substratum-conditioning factor in a manner that allows their outgrowth to be channeled along a pathway of this neurotropic substratum-associated material.
Ion-transport chain of cytochrome oxidase: the two chain-direct coupling principle of energy coupling.
Authors: Fry M , Green D E
Published: May 2006

Cytochrome oxidase (ferrocytochrome c:oxygen oxidoreductase, EC 1.9.3.1) couples the aerobic oxidation of ferrocytochrome c to the cyclical transport of monovalent cations or to the active transport of monovalent and divalent cations. This transport capability is mediated by an intracomplex ion-transport chain of two protein-bound molecules of cardiolipin per molecule of cytochrome oxidase. Cardiolipin in a two-phase system shows the identical ionophoric pattern as does the cytochrome oxidase coupled system. A molecular model of the cardiolipin chain suggests the possibility of a cage-like structure through which cations can be transferred from phosphate group to phosphate group. The ion-transport chain and the electron-transport chain are anchored to the same set of subunits (I+IV); the close proximity of the two chains argues for the direct coupling of electron and cation flow. The ion-transport chain of cytochrome oxidase provides an introduction to the molecular mechanisms by which ions are moved across membranes in energy-coupling systems.
Relationship of GIX antigen expression to the glycosylation of murine leukemia virus glycoprotein.
Authors: Rosner M R , Tung J S , Hopkins N , Robbins P W
Published: May 2006

The GIX antigen, which is expressed on the surface of thymocytes of certain mouse strains, is an antigenic determinant of the major envelope glycoprotein of murine leukemia virus (gp70). Although GIX is expressed in some mouse strains that appear to be free of virus, the antigen can also be induced in GIX- mice by infection with particular murine leukemia viruses (termed GIX+). We have investigated the envelope gene products from two closely related viruses that differ in their GIX phenotype. Analysis of the envelope protein precursors by polyacrylamide gel electrophoresis and endoglycosidase treatment indicated that the GIX+ viral protein contained six oligosaccharide chains, whereas the GIX- viral protein contained seven. The observed differences in gel electrophoretic mobilities and glycopeptide profiles of the respective glycosylated envelope gene cleavage products (gp70) may be accounted for by the presence of an additional oligosaccharide chain on the gp70 of the GIX- virus. No differences between the apparent molecular weights of the nonglycosylated product of the envelope gene (p15E) were detected. These results suggest that the GIX- virus codes for an extra glycosylation site relative to the GIX+ virus, and this oligosaccharide chain is present both on the envelope gene precursor (Prenv) and on the major cleavage product (gp70). Recent nucleotide sequence analyses of selected RNase T1 oligonucleotides from the genomes of viruses that differ in GIX phenotype have similarly suggested that there may be a correlation between the GIX- phenotype and an extra glycosylation site [Donis-Keller, H., Rommelaere, J., Ellis, R. W. & Hopkins, N. (1980) Proc. Natl. Acad. Sci. USA 77, 1642-1645]. The results of these two different approaches raise the possibility that the presence of an additional oligosaccharide chain on gp70 may, either directly or indirectly, mask the expression of the GIX antigen on the surfaces of thymocytes and virus-infected cells.
Site exclusion and sequence specificity in binding of 9-aminoacridine to the deoxytetranucleotide dpApGpCpT.
Authors: Young P R , Kallenbach N R
Published: May 2006

The interaction of the mutagenic dye 9-aminoacridine (9AA) with the self-complementary tetranucleotide dpApGpCpT has been studied by a combination of proton NMR titrations and thermal denaturation experiments. A minimum of three complexes of well-defined stoichiometry can be demonstrated in this system. Complex I is a 1:2 9AA/tetranucleotide structure occurring in the presence of excess tetranucleotide. The dye appears to intercalate within the GpC/GpC site of a tetranucleotide duplex. Complex II is a 2:2 9AA/tetranucleotide structure, with two dyes intercalated at the ApG/CpT sites of the duplex. Complex III is a low-temperature 4:2 9AA/tetranucleotide structure containing two dye molecules stacked over the terminal A-T residues of the duplex in addition to those present in complex II. These results show that both sequence selectivity and site exclusion can occur in this model system.
Purification and properties of the double-stranded RNA-activated eukaryotic initiation factor 3 kinase from rabbit reticulocytes.
Authors: Grosfeld H , Ochoa S
Published: May 2006

The double-stranded RNA (dsRNA)-activated protein kinase (DAI) that phosphorylates the alpha subunit of the eukaryotic initiation factor eIF-2 and inhibits chain initiation has been isolated from rabbit reticulocyte lysates. The nonactivated enzyme or the enzyme partially activated by incubation with low levels of dsRNA (pro-DAI) could be purified only to a slight extent. However, the enzyme that was fully activated by incubation with both dsRNA and ATP was purified to near homogeneity. Active DAI is a phosphoprotein with an apparent subunit mass of 68,000 daltons. It can phosphorylate histone as well as the alpha subunit of eIF-2. Our results suggest that, after interaction with dsRNA, the enzyme phosphorylates itself and is thereby activated to phosphorylate alpha eIF-2 and histone.
Escherichia coli RNA polymerase in vitro mimics simian virus 40 in vivo transcription when the template is viral nucleoprotein.
Authors: Jakobovits E B , Saragosti S , Yaniv M , Aloni Y
Published: May 2006

We have used a low-salt detergent-free extraction procedure on cells infected with simian virus 40 to obtain viral nucleoprotein late after infection. Addition of EScherichia coli RNA polymerase and ribonucleotide triphosphates to the viral minichromosomes permitted transcription of RNA from viral templates. This synthesis was initiated predominantly within a fragment of DNA spanning 0.67 to 0.76 map unit on the genome. The synthesis from this region proceeded primarily along the "late" strand in a clockwise direction. These results were in contrast to the synthesis obtained with naked viral DNA in which initiation occurred on other regions of the genome and from which transcription proceeded counterclockwise along the early strand. These findings indicate that the nucleoprotein template or factors tightly associated with it may be responsible for site(s) and strand selection in transcription of simian virus 40.
Regulatory coupling of nitrate and sulfate assimilation pathways in cultured tobacco cells
Authors: Reuveny Ziva , Dougall Donald K. , Trinity Philip M.
Published: May 2006

When cultured tobacco cells are provided growth-limiting concentrations of sulfur as sulfate, the rate of development of nitrate reductase (NADH:nitrate oxidoreductase, EC 1.6.6.1) is proportional to the initial sulfate concentration. When the cells are provided growth-limiting concentrations of nitrogen as nitrate, the rate of derepression of ATP sulfurylase (ATP:sulfate adenylyltransferase, EC 2.7.7.4) is proportional to the initial nitrate concentration. These results are taken to be indicative of a reciprocal regulatory coupling between the nitrate and sulfate assimilation pathways.
Production and release of plasminogen by isolated perfused rat liver.
Authors: Saito H , Hamilton S M , Tavill A S , Louis L , Ratnoff O D
Published: May 2006

In view of conflicting evidence for a major hepatic role in the synthesis of circulating plasminogen, the precursor of the fibrinolytic enzyme plasmin, we carried out the present study with a sensitive assay in order to measure the accumulation of small quantities of plasminogen in a recycling rat liver perfusion system. We have purified plasminogen from Sprague-Dawley rat plasma and have raised a monospecific antiserum against it in rabbits. Isolated rat liver perfusions were performed with an oxygenated recycling perfusate consisting of a perfluorotributylamine/Pluronic F-68 emulsion (Fluosol 43) free of plasma proteins and blood cells. The system was shown to be capable of synthesizing albumin and transferrin. The cumulative appearance of plasminogen in the perfusate was measured by a sensitive, specific radioimmunoassay. Plasminogen concentration increased progressively during the first 2 hr of perfusion; the observed average net synthesis in five separate experiments was approximately 35 microgram/hr per 100 g of body weight. Exposure of the perfused liver to 18 microM cycloheximide inhibited additional increase in the titer of plasminogen. Evidence for de novo synthesis was provided by the incorporation of 14C-labeled leucine into specific immunoprecipitates of plasminogen and the inhibition of this incorporation by cycloheximide. Analysis of the immunoprecipitates by sodium dodecyl sulfate/polyacrylamide gel electrophoresis revealed a single peak of radioactivity corresponding to Mr of 82,000. These data indicate that the liver is a major site of plasminogen production.
Mechanism of calcium current modulation underlying presynaptic facilitation and behavioral sensitization in Aplysia.
Authors: Klein M , Kandel E R
Published: May 2006

Behavioral sensitization of the gill-withdrawal reflex of Aplysia is caused by presynaptic facilitation at the synapses of the mechanoreceptor sensory neurons of the reflex onto the motor neurons and interneurons. The presynaptic facilitation has been shown to be simulated by serotonin (the putative presynaptic facilitatory transmitter) and by cyclic AMP and to be accompanied by an increase in the Ca2+ current of sensory neuron cell bodies exposed to tetraethylammonium. This increase in the Ca2+ current could result from either a direct action on the Ca2+ channel or an action on an opposing K+ current. Here we report voltage clamp experiments which indicate that the increase in Ca2+ current associated with presynaptic facilitation results from a decrease in a K+ current. Stimulation of the connective (the pathway that mediates sensitization) or application of serotonin causes a decrease in a voltage-sensitive, steady-state outward current measured under voltage clamp as well as an increase in the transient net inward and a decrease in the transient outward currents elicited by brief depolarizing command steps. The reversal potential of the steady-state synaptic current is sensitive to extracellular K+ concentration, and both the steady-state synaptic current and the changes in the transient currents are blocked by K+ current blocking agents and by washout of K+. These results suggest that serotonin and the natural transmitter released by connective stimulation act to decrease a voltage-sensitive K+ current. The decrease in K+ current prolongs the action potential, and this in turn increases the duration of the inward Ca2+ current and thereby enhances transmitter release.
Stereochemical consequences of dynamic gearing in substituted bis(9-triptycyl) methanes and related molecules
Authors: Hounshell W. Douglas , Johnson Constance A. , Guenzi Alberto , Cozzi Franco , Mislow Kurt
Published: May 2006

Empirical force-field calculations show that bis(9-triptycyl)methane has a

C
s

ground state and that the securely meshed triptycyl groups undergo nearly unhindered cogwheel rotation through a
C
2
transition state, with an activation energy of ≈1.0 kcal mol
-1
. These features lead to note-worthy stereochemical attributes in appropriately substituted derivatives and analogs. Bis(9-triptycyl)carbinol has been prepared as an example of a compound that is chemically achiral, even though all conformations are chiral under the constraint of gear meshing. It is shown that, under the same constraint, ring substitution of either compound (or analogous systems) may lead to residual stereoisomerism. A permutational analysis of chemical isomers and isomerizations for every possible type of substitution pattern gives an enumeration of residual stereoisomers under the operation of various gearing and nongearing modes and provides information essential for a choice among mechanistic alternatives for a given isomer count.
Spacer DNA sequences upstream of the T-A-T-A-A-A-T-A sequence are essential for promotion of H2A histone gene transcription in vivo.
Authors: Grosschedl R , Birnstiel M L
Published: May 2006

The control region of a sea urchin H2A histone gene may be functionally dissected into at least three DNA segments, which we have termed modulator, selector, and initiator elements. While the initiator and in particular the selector containing the T-A-T-A-A-A-T-A sequence are specificity elements that dictate the generation of faithful 5' ends to H2A mRNA, the modulators control the rate at which these specificity elements operate [Grosschedl, R. & Birnstiel, M. L. (1980) Proc. Natl. Acad. Sci. USA 77, 1432-1436]. By functional tests of in vitro mutated histone DNA in the Xenopus oocyte we have now discovered that the segment E of the A+T-rich spacer DNA lying at a considerable distance upstream of the conservative T-A-T-A-A-A-T-A sequence is a strong modulator element of H2A gene transcription. Deletion of this element creates a 15- to 20-fold H2A-specific down mutation. Segment E by itself cannot elicit initiation of transcription except in coordination with the prelude sequence of the H2A gene. The nucleotide sequence of the relevant spacer element showing modulator activity has been determined and found to contain a pattern of T and A runs as well as a series of inverted repeats. Additional pre-H2A spacer mutants, including a spacer inversion mutant, have been constructed in vitro, that, when injected into the oocyte nucleus, modulate the expression of the H2A gene by an overall factor as large as 100. Other factors controlling promoter activity are discussed.
Kinetic aspects of cycloheximide-induced reversal of adrenocorticotropin effects on steroidogenesis and adrenal phospholipids in vivo.
Authors: Farese R V , Sabir M A , Larson R E
Published: May 2006

Intraperitoneal injection of maximally effective doses of corticotropin(1-24) [ACTH(1-24)] provoked maximal increases in rat adrenal phospholipids as follows: phosphatidic acid within 1.5-2 min, phosphatidylinositol and phosphatidylglycerol within 4-6 min, and polyphosphoinositides and corticosterone within 5-15 min. Continued maximal adrenal stimulation by ACTH(1-18) treatment caused sustained increases in adrenal phosphatidic acid, phosphatidylinositol, phosphatidylglycerol, polyphosphoinositides, and corticosterone. Treatment with cycloheximide during this steady-state caused rapid decreases in all of these substances to basal levels. The observed half-lives of adrenal phosphatide acid, phosphatidylinositol, polyphosphoinositides, phosphatidylglycerol, and corticosterone during cycloheximide inhibition were 0.15, 1.0, 1.7, 3.3, and 3.5 min, respectively. Calculated production rates during maximal ACTH stimulation were 1060, 991, 90, 34, and 41 nmol/g of tissue per min, respectively. These findings suggest that (i) an initial effect of ACTH on de novo synthesis of phosphatidic acid can account for all subsequently observed increases in other phospholipid derivatives of CDP-diacylglycerol, (ii) a labile protein is required for the ACTH-induced increase in phosphatidic acid, (iii) the phosphatidate leads to polyphosphoinositide-polyglycerophospholipid pathway is rapidly and dramatically responsive to hormonal stimulation, (iv) changes in steroidogenesis correlate well with changes in this phospholipid pathway, and (v) stimulation of this pathway is rapidly reversible.
Isolation and amino acid sequence of gamma-lipotropin from human pituitary glands.
Authors: Li C H , Chung D , Yamashiro D
Published: May 2006

gamma-Lipotropin has been purified to homogeneity from human pituitary glands. It consists of 56 amino acids with one residue each of Trp, Thr, Val, Tyr, and Phe. The amino acid sequence has been determined as follows: H-Glu-Leu-Thr-Gly-Gln-Arg-Leu-Arg-Gln-Gly-Asp-Gly-Pro-Asn-Ala-Gly-Ala-Asp-Asp-G ly-Pro-Gly-Ala-Gln-Ala-Asp-Leu-Glu-His-Ser-Leu-Leu-Val-Ala-Ala-Glu-Lys-Lys-Asp- Glu-Gly-Pro-Tyr-Arg-Met-Glu-His-Phe-Arg-Trp-Gly-Ser-Pro-Pro-Lys-Asp-OH. Comparison with the structure of the ovine and porcine hormones reveals that the 23-amino-acid sequence at the COOH terminus is highly conserved in evolution.
Molecular evidence for genetic exchanges among ribosomal genes on nonhomologous chromosomes in man and apes.
Authors: Arnheim N , Krystal M , Schmickel R , Wilson G , Ryder O , Zimmer E
Published: May 2006

We have found that human and ape ribosomal genes undergo concerted evolution involving genetic exchanges among nucleolus organizers on nonhomologous chromosomes. This conclusion is based upon restriction enzyme analysis of the ribosomal gene families in man and five ape species. Certain structural features were found to differ among (but not within) species even though the ribosomal genes have a multichromosomal distribution. Genetic exchanges among nucleolus organizer regions may be related to the well-known phenomenon of acrocentric chromosome associations observed in man and apes. Length variation in a region of the nontranscribed spacer was found in both chimpanzee species we examined. The nature of this length variation was found to be identical to that previously described in man. The origin of the length variation and its polymorphism within these three species might be explained by unequal alignment and unequal cross-over among the ribosomal genes. An especially surprising finding was a nucleotide sequence polymorphism present in each individual human and ape we examined. Some ribosomal genes of each individual have a HindII site in the 28S gene about 800 base pairs from the EcoRI site in this gene. The remaining 28S genes lack this HindII site. The presence of this polymorphism within individuals of every species we examined suggests that it has been maintained by natural selection.
Replication of plasmids from Staphylococcus aureus in Escherichia coli.
Authors: Goze A , Ehrlich S D
Published: May 2006

Plasmid pBR322 derives from plasmid ColE1 and does not replicate in Escherichia coli strains lacking DNA polymerase I. Hybrids between pBR322 and a plasmid isolated from Staphylococcus aureus, pC194, replicate in such E. coli strains, provided that the pC194 replication region is intact. Inactivation of the pBR322 replication region does not interfere with the replication of hybrids in E. coli. Hybrids between pBR322 and two other plasmids from S. aureus, pT127 and pUB112, and replicate at the restrictive temperature in E. coli having thermosensitive DNA polymerase I. Similar hybrids involving pC221 and pHV400, plasmids from S. aureus and Bacillus subtilis, respectively, do not replicate under such conditions. These results show that some plasmids from a Gram-positive bacterium, S. aureus, can replicate in a Gram-negative one, E. coli.
Bicuculline enhances a negative component and diminishes a positive component of the visual evoked cortical potential in the cat.
Authors: Zemon V , Kaplan E , Ratliff F
Published: May 2006

Visual evoked potentials (VEPs), elicited by modulation of luminance of homogeneous fields of light, were recorded from the scalp and from the surface of the visual cortex of cats before and after topical application of bicuculline to the cortex. The application of this drug drastically altered the VEP: the amplitude of a normally small negative component was increased greatly, and a normally prominent late positive component was diminished. Bicuculline is known to block the action of gamma-aminobutyric acid, which is thought to be the primary inhibitory neurotransmitter in the visual cortex. We suggest, therefore, that the affected negative wave reflects an excitatory process in the visual cortex and that the affected late positive wave reflects an intracortical inhibitory process.
A role for cyclic AMP in expression of developmentally regulated genes in Dictyostelium discoideum.
Authors: Landfear S M , Lodish H F
Published: May 2006

Starved cells of Dictyostelium discoideum begin to synthesize a new class of developmentally regulated proteins at about 13 hr of the 24-hr developmental program, concomitant with the formation of tips on the tight cell aggregates [Alton, T. H. & Lodish, H. F. (1977) Dev. Biol. 60, 180--206]. Continued synthesis of these proteins is normally dependent upon the integrity of the multicellular aggregates, because cells that have been disaggregated at 13 hr and shaken in suspension for 5 hr do not make these proteins. We show here that addition of 20 microM cyclic AMP to suspension cultures of disaggregated 13-hr cells caused synthesis of most of these late proteins to be maintained. Translation in an in vitro wheat germ system of total cellular RNA isolated from these cyclic AMP-stimulated suspension cells, or from normal aggregates, generated several proteins that were not encoded by the RNA isolated from equivalent suspension cells which had not been treated with cyclic AMP or from preaggregation cells. We conclude that cyclic AMP has a direct role in maintaining the synthesis of aggregation-dependent Dictyostelium proteins and in maintaining the level of the corresponding mRNAs.
Linkage of genes for adult alpha-globin and embryonic alpha-like globin chains.
Authors: Whitney J B , Russell E S
Published: May 2006

In alpha-thalassemia, the genetic locus for the alpha chains of adult hemoglobin is not expressed. We have examined the hemoglobins of a number of individual mouse embryos heterozygous for a particular alpha-thalassemia (Hbath-J) and find no decrease in the proportion of hemoglobins containing the alpha chain as compared to the hemoglobin containing the alpha-like embryonic globin chain. This result suggests that the locus for this embryonic alpha-like chain is inactivated or deleted in these embryos as well. Because a single mutational event inactivated adult and embryonic loci, we conclude that they are probably closely linked to one another on the same chromosome. We also present evidence that an unusual hemoglobin in the blood of these embryos is composed only of an embryonic beta-like chain, and is thus analogous to the hemoglobin H (beta 4 tetramer) of adult alpha-thalassemics.
Partial amino acid sequence of human factor D:homology with serine proteases.
Authors: Volanakis J E , Bhown A , Bennett J C , Mole J E
Published: May 2006

Human factor D purified to homogeneity by a modified procedure was subjected to NH2-terminal amino acid sequence analysis by using a modified automated Beckman sequencer. We identified 48 of the first 57 NH2-terminal amino acids in a single sequencer run, using microgram quantities of factor D. The deduced amino acid sequence represents approximately 25% of the primary structure of factor D. This extended NH2-terminal amino acid sequence of factor D was compared to that of other trypsin-related serine proteases. By visual inspection, strong homologies (33--50% identity) were observed with all the serine proteases included in the comparison. Interestingly, factor D showed a higher degree of homology to serine proteases of pancreatic origin than to those of serum origin.
Sensory neurons in culture: Changing requirements for survival factors during embryonic development
Authors: Barde Y.-A. , Edgar D. , Thoenen H.
Published: May 2006

The effect of nerve growth factor (NGF) and medium conditioned by glioma cells (GCM) on the survival of chicken sensory neurons in culture was investigated. Neurons were isolated from embryos 8 days (E8) to 16 days (E16) old and the proportion of surviving neurons was determined after 2 days in culture. In the absence of NGF or GCM, essentially no neurons survived at any age. In the presence of NGF, survival increased from 25% of the neurons at E8 to 40% between E10 and E12 and then decreased to background level (5%) at E16. In contrast, in the presence of GCM, survival increased continuously from 10% of the neurons at E8 to 75% at E16. At early developmental stages, the effect of NGF and GCM together was greater than the sum of their individual effects: at E8, about 80% of the neurons survived, double the number expected for a simple additive effect. Thus, a significant proportion of chicken neurons from dorsal root ganglia require both NGF and GCM for survival, and this may well include neurons from the ventro-lateral population, which do not respond to NGF alone. As neurons matured, the double requirement progressively decreased and, by E16, NGF no longer increased the number of neurons over that surviving in response to GCM alone. The facts that rat brain extracts mimicked the effect of GCM and that the potency of the brain extracts of rat in the postnatal period increased in parallel with the development of the glial cells suggest that glial cells produce a factor(s) both immunologically and functionally different from NGF which supports the survival of sensory neurons.
Leptinotarsin: A presynaptic neurotoxin that stimulates release of acetylcholine
Authors: McClure William O. , Abbott Bernard C. , Baxter Daniel E. , Hsiao Ting H. , Satin Leslie S. , Siger Alvin , Yoshino Jun E.
Published: May 2006

Leptinotarsin, a toxin found in the hemolymph of the beetle
Leptinotarsa haldemani
, can stimulate release of acetylcholine from synaptic termini. Leptinotarsin causes an increase in the frequency of miniature end plate potentials (mepps) of the rat phrenic nerve-diaphragm preparation. The increase in the frequency of mepps induced by leptinotarsin is biphasic: about 10% of the total mepps are released in an initial burst that lasts about 90 sec, after which the remaining mepps are released over a period of 10-20 min. Tetrodotoxin has no effect upon the release induced by leptinotarsin, but low-Ca
2+
conditions abolish the first phase. The two phases of release may represent two presynaptic pools of acetylcholine, both of which can be released in quantized form. In a second study, rat brain synaptosomes were incubated with [
3
H]choline and were immobilized on Millipore filters. Leptinotarsin induced release of [
3
H]acetylcholine from this preparation, confirming the release seen by using neurophysiological methods. The ability of leptinotarsin to induce release from either intact nerve terminals or synaptosomes was abolished when the toxin was heated. The releasing activity of leptinotarsin from synaptosomes was also partially dependent upon the presence of Ca
2+
in the perfusing solution. Release from synaptosomes followed first-order kinetics, and was not inhibited by commercial antibodies to black widow spider antigens. The data suggest that leptinotarsin acts as a presynaptic neurotoxin and may be of value as a mechanistic probe in understanding the storage and release of neurotransmitters.
N,N'-dicyclohexylcarbodiimide binds specifically to a single glutamyl residue of the proteolipid subunit of the mitochondrial adenosinetriphosphatases from Neurospora crassa and Saccharomyces cerevisiae.
Authors: Sebald W , Machleidt W , Wachter E
Published: May 2006

The N,N'-dicyclohexylcarbodiimide-binding proteolipid subunit of the mitochondrial adenosinetriphosphatases (ATP phosphohydrolase, EC 3.6.1.3) of Neurospora crassa and Saccharomyces cerevisiae were purified from mitochondria incubated with the radioactively labeled inhibitor. The specifically labeled subunit was cleaved with cyanogen bromide and N-bromosuccinimide, and the resultant fragments were separated by gel chromatography in the presence of 80% (vol/vol) formic acid. The N,N'-dicyclohexylcarbodiimide label was recovered in each organism exclusively in a 17-residue fragment. Further analysis by automated solid-phase Edman degradation revealed that the bound label was present at only one position, corresponding to a glutamyl residue. The N,N'-dicyclohexylcarbodiimide-modified glutamyl residue is the only identical acidic position in both proteins and occurs in the middle of a hydrophobic sequence of about 25 residues.
Formylmethionyl-tRNA alters RNA polymerase specificity.
Authors: Debenham P G , Pongs O , Travers A A
Published: May 2006

Escherichia coli fMet-tRNAfMet alters the pattern of promoter selection of E. coli RNA polymerase (RNA nucleotidyltransferase, nucleosidetriphosphate:RNA nucleotidyltransferase; EC 2.7.7.6), affecting RNA synthesis from the rRNA, suIII+tRNA, and lac promoters in different ways. The in vitro synthesis of the stable RNA species is selectively decreased, whereas that of lac RNA from both the wild-type and mutant UV5 promoters is selectively increased at high ionic strength. The functional effect of fMet-tRNAfMet resembles that of the nucleotide guanosine 3'-diphosphate 5'-diphosphate (ppGpp). This nucleotide competes with the binding of fMet-tRnafMet to RNA polymerase.
Initiation of DNA replication by the Escherichia coli dnaG protein: evidence that tertiary structure is involved.
Authors: Sims J , Benz E W
Published: May 2006

The dnaG protein of Escherichia coli initiates DNA replication by synthesizing primer oligonucleotides for elongation by DNA polymerae. The experiments reported here probe the nature of the nucleic acid element recognized by the dnaG protein. Three well-separated groups of nucleotides within the negative-strand origin of the single-stranded phage phi K are protected by the dnaG protein against nuclease digestion. DNA as far as 115 bases from the start site of primer synthesis is involved in binding of the dnaG protein to the replication origin. One molecule of dnaG protein could protect all of these nucleotides if the DNA were folded into a higher-order tertiary structure. Protection of the phi K origin by dnaG protein requires DNA binding protein, and it does not occur if the group of protected nucleotides most distant from the start site is removed from the template. There is no binding of dnaG protein to the complementary strand of the phi K origin-region DNA. The observed protection of the positive strand is due to a functional nucleic acid-protein complex.
Spectroscopic studies of the protein-methylglyoxal adduct.
Authors: McLaughlin J A , Pethig R , Szent-Györgyi A
Published: May 2006

Spectroscopic measurements are reported for the effects of pH, time, solvent, and chemical modification of arginine and lysine side chains on the reaction of proteins with methylglyoxal. The reaction responsible for the appearance of a brown coloration and increased submolecular electronic activity in the proteins involves the epsilon-amino groups of the lysine residues. It is concluded that the primary step in the reaction involves the formation of a Schiff base linkage between the lysine side chain and methylglyoxal. These findings reaffirm the concept that, by the formation of Schiff bases, aldehydes can act as electron acceptors in charge transfer interactions with proteins.
Integrated and free viral DNA in hamster tumors induced by BK virus.
Authors: Chenciner N , Meneguzzi G , Corallini A , Grossi M P , Grassi P , Barbanti-Brodano G , Milanesi G
Published: May 2006

BK virus (BKV)-induced tumors in hamsters were investigated for the presence of viral DNA by the blot-transfer hybridization technique. Several viral genomes per cell were found in tumor tissues and in their derived cell lines and clones. Most of the detected viral genomes were integrated into the cellular DNA, but some tumors also contained free viral DNA sequences. Integration patterns were different from each other, and many different integration sites were available on the cellular or on the viral DNA or on both. Typical features of integration patterns were found in ependymomas, which were the most frequent (72%) among BKV-induced tumors. Readily detectable viral DNA sequences were only found in neoplastic tissues, but traces of BKV DNA were also present in the apparently normal portion of the brain of an animal that had developed an ependymoma and in the brain (but not in the liver) of another animal 15 days after virus inoculation. A cell line and a single-cell clone derived from a tumor had hybridization patterns considerably simpler that the pattern of the original tumor, lacking several integrated viral genomes and all free viral sequences.
Calcium and microtubule dependence for increased ornithine decarboxylase activity stimulated by β-adrenergic agonists, dibutyryl cyclic AMP, or serum in a rat astrocytoma cell line
Authors: Gibbs Jackson B. , Hsu Chung-Yi , Terasaki Wesley L. , Brooker Gary
Published: May 2006

Ornithine decarboxylase (ODCase; L-ornithine carboxy-lyase; EC 4.1.1.17) activity was increased 5-20 fold above basal activity by
N
6
,
O
2′
-dibutyryl cyclic AMP, isoproterenol, epinephrine, or fetal calf serum in confluent C6-2B rat astrocytoma cells. Serum increased ODCase activity by a mechanism apparently independent of cyclic AMP because it decreased intracellular cyclic AMP. Calcium ethylene glycol bis(β-aminoethyl ether)-
N,N,N′,N′
-tetraacetic acid (EGTA) buffers (pCa = 6.4) reduced basal ODCase activity and blocked the increase in activity by β-adrenergic agonists, dibutyryl cyclic AMP, or serum. Readdition of calcium to pCa = 4.0 restored the ability of the cells to respond to these agents. The rise in ODCase activity stimulated by isoproterenol, dibutyryl cyclic AMP, or serum was also blocked by the microtubule disrupting agents, vinblastine and colchicine, and by the microfilament disrupting agent, cytochalasin B. Lumicolchicine, an analog of colchicine that does not disrupt microtubules, was ineffective. The microtubule and microfilament disrupting agents and EGTA had no effect on the intracellular accumulation of cyclic AMP. Cycloheximide inhibited protein synthesis >95% within 30 min, and caused an immediate decline of stimulated ODCase activity with a half-time of 20-30 min. The inhibition of ODCase activity by colchicine or EGTA was distinct from that seen with cycloheximide and could not be correlated to their effects on general protein synthesis. Colchicine or EGTA each caused identical rates of decline in ODCase activity with a half-time of 20-30 min after an initial lag period of about 60 min.
Leader sequences of Strongylocentrotus purpuratus histone mRNAs start at a unique heptanucleotide common to all five histone genes.
Authors: Sures I , Levy S , Kedes L H
Published: May 2006

We have determined the sequence of the untranslated leader nucleotides of all five histone mRNAs from Strongylocentrotus purpuratus by the dideoxy chain termination method. Total polysomal RNA from sea urchin embryos was used as a substrate for cDNA synthesis primed by specific DNA restriction fragments. Each of the primers was derived from the 5'-terminal part of the coding region for a different histone protein. The five histone mRNA leader sequences are different in length and primary structure. The 5' termini of all five histone mRNAs coincide with the unique heptanucleotide Py-Py-A-T-T-C-Pu in genomic DNA. This sequence, which defines the start of the individual histone mRNAs, is preceded by the A+T-rich octanucleotide identified in front of all eukaryotic structural genes where sequences have been determined to date.
Additional component required for activity and reconstitution of light-activated vertebrate photoreceptor GTPase.
Authors: Shinozawa T , Uchida S , Martin E , Cafiso D , Hubbell W , Bitensky M
Published: May 2006

A light-activated GTPase that functions as a component of the rhodopsin-linked, light-activated phosphodiesterase (PDEase) system in vertebrate photoreceptors has been reported. In our efforts to purify photoreceptor GTPase we encountered another component (which we call "helper" or "H" component) whose presence is required for expression of light-activated GTPase activity. We report here the characterization of this heat-labile, macromolecular factor and that the presence of helper is absolutely required for light- and rhodopsin-dependent activation of photoreceptor GTPase. Of equal importance, we find that the "G" component (which requires the presence of H for expression of GTPase activity) can bind GTP and can support light- and GTP-dependent PDEase activation in the absence of H component. These data support a model in which GTP binding to G component is a necessary condition for PDEase activation. Hydrolysis of GTP at the G activator locus (an H-dependent activity) is a regulatory event which reverses PDEase activation. The complexity of this regulatory mechanism provides opportunities for signal modulation and amplification.
Reactivation of ribosomal RNA genes in human-mouse hybrid cells by 12-O-tetradecanoylphorbol 13-acetate.
Authors: Soprano K J , Baserga R
Published: May 2006

The effect of the potent tumor promoter 12-O-tetradecanoylphorbol 13-acetate (TPA) on the expression of rRNA genes was studied in human greater than mouse hybrid cells (55-54 cells). These hybrids retain the rRNA genes of both parent species but express only human rRNA. 55-54 cells were treated with either TPA (1-100 nM), phorbol (0.01-1 micro M) or phorbol 13,20-diacetate (0.01-1 micro M). After 24 hr the cells were harvested and the extracted rRNA was analyzed by agarose/2.4% polyacrylamide gel electrophoresis. The results show that only the TPA-treated hybrid cells synthesized both human and mouse 28S rRNA. Untreated cells and cells treated with phorbol or phorbol 13,20-diacetate synthesized only human 28S rRNA. The reactivation of silent rRNA genes by TPA was not restricted to mouse rRNA genes. In mouse-human hybrids in which both human and mouse rRNA genes are present but only the mouse genes are expressed, TPA treatment led to reactivation of the silent human rRNA genes. Although tumor promoters are generally believed to alter gene expression, we have found a specific gene whose transcription is modified by treatment with TPA.
T-cell-dependent B-cell stimulation is H-2 restricted and antigen dependent only at the resting B-cell level.
Authors: Andersson J , Schreier M H , Melchers F
Published: May 2006

Cloned lines of helper thymus-derived (T) cells produce help for bone marrow-derived (B) cell growth and Ig secretion in the presence of histocompatible adherent cells and of specific antigen. This help stimulates histocompatible as well as histoincompatible B-cell blasts polyclonally. Thus, neither antigen nor histocompatibility, but antigen-unspecific factor(s) for growth and Ig secretion are required to stimulate a B-cell blast through the next round of division. On the other hand, only histocompatible, resting, small B cells, and only those binding their specific antigen, can be stimulated by antigen-activated T-cell help to initiate growth and Ig secretion. The preference of the resting B cells for such collaboration with T-cell help is mapped to the K end of the H-2 histocompatibility locus, and probably constitutes the antigen expressed on B cells by the immune response (I) region. It appears that a resting B cell is excited by the binding of specific antigen to surface Ig and by the interaction of its surface Ia antigen with helper T cells. After this dual recognition the excited B cell can be stimulated by the antigen-unspecific factor(s) generated by the interaction of helper T-cells, adherent cells, and antigen to initiate replication.
Bathymetry and temperature of some glacial lakes in Wyoming
Authors: Leopold Luna B.
Published: May 2006

On the west flank of the Wind River Mountains, Wyoming, are several large lakes occupying glacially scoured depressions dammed by terminal moraines. Fremont, Willow, and New Fork Lakes, having maximal depths of 185, 85, and 62 m, respectively, are not only deep, but in 1970-1978 they had no measurable coliform. They have exceptionally low values of total dissolved solids; Fremont Lake has only 12.8 mg/liter, probably the second most dilute large lake in coterminus United States. Summer mixing is restricted to the uppermost 10 m, below which the lakes are essentially isothermal at the maximum density temperature, about 3.9°C.
In vitro expression of Escherichia coli ribosomal protein genes: autogenous inhibition of translation.
Authors: Yates J L , Arfsten A E , Nomura M
Published: May 2006

Escherichia coli ribosomal protein L1 (0.5 micro M) was found to inhibit the synthesis of both proteins of the L11 operon, L11 and L1, but not the synthesis of other proteins directed by lambda rifd 18 DNA. Similarly, S4 (1 micro M) selectively inhibited the synthesis of three proteins of the alpha operon, S13, S11, and S4, directed by lambda spcI DNA or a restriction enzyme fragment obtained from this DNA. S8 (3.6 micro M) also showed preferential inhibitory effects on the synthesis of some proteins encoded in the spc operon, L24 and L5 (and probably S14 and S8), directed by lambda spcl DNA or a restriction enzyme fragment carrying the genes for these proteins. The inhibitory effect of L1 was observed only with L1 and not with other proteins examined, including S4 and S8. Similarly, the effect of S4 was not observed with L1 or S8, and that of S8 was not seen with L1 or S4. Inhibition was shown to take place at the level of translation rather than transcription. Thus, at least some ribosomal proteins (L1 S4, and S8) have the ability to cause selective translational inhibition of the synthesis of certain ribosomal proteins whose genes are in the same operon as their own. These results support the hypothesis that certain free ribosomal proteins not assembled into ribosomes act as "autogenous" feedback inhibitors to regulate the synthesis of ribosomal proteins.
Translocation of phospholipids from the inner to the outer membrane of Escherichia coli.
Authors: Donohue-Rolfe A M , Schaechter M
Published: May 2006

The translocation of lipids from the inner to the outer membrane of Escherichia coli has been investigated by pulse-chase experiments. After a pulse with [2-3H]glycerol, the specific activity of the newly synthesized [3H]phosphatidylethanolamine was 5 times greater in the inner than in the outer membrane. During the chase, [3H]phosphatidylethanolamine was translocated to the outer membrane. At 37 degrees C, the half-life for translocation was 2.8 min. This rate was not influenced by alteration in the cellular growth rate at 37 degrees C. Altering the cellular growth temperature had a pronounced effect on the rate of phosphatidylethanolamine translocation. Energy inhibitors that deplete the protonmotive force markedly inhibited the translocation. Translocation was not affected by inhibitors of ATP, protein, or lipid synthesis. Phosphatidylglycerol and cardiolipin are transfocated very rapidly, with half-lives shorter than 30 sec.
Biosynthesis of precursor corticotropin/endorphin-, corticotropin-, alpha-melanotropin-, beta-lipotropin-, and beta-endorphin-like material by cultured neonatal rat hypothalamic neurons.
Authors: Liotta A S , Loudes C , McKelvy J F , Krieger D T
Published: May 2006

Enzymatically dispersed hypothalamic cells derived from 15-day-old female rats were maintained in tissue culture for 4 days and then incubated for 2 hr in the presence of [35S]methionine. After such incubation, cell extracts contained multiple forms of 35S-labeled products that were specifically bound by immobilized affinity-purified antisera to corticotropin and beta-endorphin. Sequential use of these immobilized antisera revealed two molecular species (apparent Mr of 33,000 and 36,500) that contained both corticotropin and beta-endorphin antigenic determinants within the same molecule. Substances containing only one of these determinants were also present and co-eluted with corticotropin, alpha-melanotropin, beta-lipotropin, or beta-endorphin upon Sephadex G-50 gel filtration. Extracts of similarly labeled rat anterior and intermediate pituitary lobe cells contained two forms of the common precursor molecule corresponding to the same molecular weights estimated for the hypothalamic material and similar to it with respect to other physicochemical parameters. These data suggest that rat hypothalamus synthesizes corticotropin-related and beta-endorphin-related products via sequential cleavage of a larger common precursor molecule in a manner similar to the processing pathway demonstrated for the intermediate lobe of the pituitary.
Repeating structure of cytoplasmic poly(A)-ribonucleoprotein.
Authors: Baer B W , Kornberg R D
Published: May 2006

A repeating structure of cytoplasmic poly(A)-ribonucleoprotein is revealed by digestion with T2 RNase. A pattern of fragments that are multiples of about 27 residues is obtained. The repeating structure is readily reconstituted from purified poly(A) and cytoplasmic factors. Reconstitution is specific for poly(A), as shown by the lack of competition by poly(G), poly(C), poly(dA), and tRNA. The repeating structure is absent from the nucleus, and so appears to be formed upon transport to the cytoplasm.