bluuebunny/crossref_metadata_2025 huggingface dataset:
Enemy deterrence in the recruitment strategy of a termite: Soldier-organized foraging in
Nasutitermes costalis
Authors: Traniello James F. A.
Published: May 2006

The nasute soldiers of the neotropical termite
Nasutitermes costalis
function as scouts by exploring new terrain for food in advance of the worker caste and regulate foraging activity by laying trails composed of sternal gland pheromone. Additional soldiers are at first recruited in large numbers, and subsequently workers appear as the pheromone concentration increases. The role of the nasutes in the organization of foraging is extremely unusual for the soldier caste in social insects and appears to be a component of a foraging/defense system that controls the recruitment of foragers and effectively deters attacks by ants, the most fierce and important predators of termites.
Seismology and geodesy of the sun: Low-frequency oscillations
Authors: Dicke R. H.
Published: May 2006

The hourly averages of the solar ellipticity measured from June 13 to Sept. 17, 1966, are analyzed for indications of solar oscillations with periods in excess of 2 hr ν < 0.5 hr
-1
. Nothing significant is found for frequencies ν > 0.1 hr
-1
but for lower frequencies the power spectrum shows a very complex structure containing about 20 strong narrow peaks. The complexity is illusionary. The signal apparently consists of only two frequencies. The complexity is due to aliasing by the window function with its basic 24-hr period, with many observational days missing, and with different numbers of hourly averages for the various observational days. Both signal frequencies are apparently due to odd-degree spherical harmonic oscillations of the sun.
Identification and purification of the Lon
+
(capR
+
) gene product, a DNA-binding protein
Authors: Zehnbauer Barbara A. , Foley Edward C. , Henderson Gordon W. , Markovitz Alvin
Published: May 2006

The polypeptide product of the
lon
(
capR
) gene was identified and partially purified from bacterial strains homozygous for the
capR
+
or
capR9
(ochre mutation) alleles cloned with pSC101. A 94,000-dalton polypeptide was identified as the lon (capR) gene product. Studies of binding to DNA cellulose columns and nitrocellulose filters indicate that the capR
+
and capR9 proteins bind DNA.
Saturable acetylcholine transport into purified cholinergic synaptic vesicles.
Authors: Michaelson D M , Angel I
Published: May 2006

The uptake of [3H[acetylcholine ([3H]AcCho) into cholinergic synaptic vesicle ghosts purified from Torpedo electric organ was studied at concentration of [3H]AcCho ranging from 0.1 to 10 mM. The accumulated [3H]AcCho can be released either by hypoosmotic buffer or by low levels of the detergent Triton X-100. Kinetic analysis of the initial rate of [3H]AcCho uptake reveals temperature-dependent saturation kinetics which are best fitted by high-affinity (KTh approximately 0.3 mM) and low-affinity (KT) approximately 10 mM) vesicular [3H]AcCho transport systems. Several lines of evidence suggest that [3H]AcCho transport is mediated by vesicle-associated transport systems and not by a contaminant of other subcellular moieties such as the plasma membrane choline transport system. (i) The specific activity of the [3H]AcCho transport systems is higher in the purest vesicular fraction than in the less-pure fractions. (ii) Ghosts prepared from isolated synaptosomes manifest only low levels of low-affinity [3H]AcCho transport and no high-affinity [3H]AcCho transport. (iii) The vesicular AcCho transport systems lack some of the typical characteristics of synaptosomal choline transport, such as Na+ activation. (iv) The ratio of uptakes of [3H]AcCho and [3H]choline (10 microM) is about 5-fold higher in the pure vesicles than in isolated synaptosomal membranes. Addition of Mg2+-ATP decreases the rate of vesicular [3H]AcCho uptake by about 50%. The simultaneous addition of NaHCO3 and Mg2+-ATP results in activation of [3H]AcCho uptake to about 125% (relative to control), which is a 2.5-fold enhancement relative to the rate observed with Mg2+-ATP. The present findings demonstrate the presence of novel vesicle-associated AcCho transport systems. Their physiological role in the life cycle of the cholinergic synaptic vesicle and nerve terminal are discussed.
Fusion of Escherichia coli lacZ to the cytochrome c gene of Saccharomyces cerevisiae.
Authors: Guarente L , Ptashne M
Published: May 2006

Hybrid genes between the Escherichia coli lacZ gene and the iso-1-cytochrome c (CYC1) gene of Saccharomyces cerevisiae were constructed by recombination in vitro. Each of the hybrid genes encodes a chimeric protein with a cytochrome c moiety at the amino terminus and an active beta-galactosidase (beta-D-galactoside galactohydrolase, EC 3.2.1.23) moiety at the carboxy terminus. When these hybrids are introduced into S. cerevisiae on plasmid vectors, they direct synthesis of beta-galactosidase. beta-Galactosidase levels directed by one such plasmid display the pattern of regulation normally seen for cytochrome c (i.e., a reduction of synthesis in cells grown in glucose). This plasmid contains one codon of CYC1 fused to lacZ, and the fused gene is preceded by the 1100 nucleotides that lie upstream from CYC1. An analysis of deletions in the upstream DNA suggests that sequences required for efficient transcription initiation of CYC1 lie within the DNA segment 250--700 base pairs upstream from the start of the CYC1 coding sequence. This region is at least 130 base pairs upstream from the "Hogness box" sequence that precedes the CYC1 coding sequence.
A model for biological oscillations.
Authors: Chay T R
Published: May 2006

A model and computation for oscillatory phenomena observed in some biological processes that utilize ion gradients across a membrane is presented. The model contains two main features: (i) active H+ transport pathways in the membrane and (ii) key enzymes having a pH-dependent activity profile and either translocating H+ from outside or producing H+ as a product. With this model a very long period of oscillations, as observed in mitochondrial and circadian rhythms, could be quantitatively demonstrated.
Formycin 5'-triphosphate, a fluorescent analog of ATP, as a substrate for adenylate cyclase.
Authors: Rossomando E F , Jahngen J H , Eccleston J F
Published: May 2006

Formycin 5'-triphosphate (FoTP), a fluorescent analog of ATP, is shown to be a substrate for the membrane-bound adenylate cyclase activity [ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1] from rat osteosarcoma cells. The formation of the adenylate cyclase reaction product, 3',5'-cyclic formycin monophosphate (cFoMP), was followed by the conventional radioimmunoassay (RIA) procedure used to detect cAMP and by an assay procedure in which the reaction product was separated from the substrate by reverse-phase high-pressure liquid chromatography (HPLC) and the reaction product was detected by fluorometry. Because the HPLC--fluorometric procedure can determine the amount of cFoMP present in the reaction mixture within 6 min, the enzymatic conversion of FoTP to cFoMP can be followed directly during the course of a typical 15-min incubation. The amount of cFoMP detected by this procedure was found to be within 2% of the values obtained by the RIA. The rate of product formation with FoTP was similar to that observed with ATP and the activity of the enzyme was enhanced about 5-fold with guanyl-5'-yl imidodiphosphate when either ATP or FoTP was used as the substrate. Kinetic studies revealed values for the Vmax of 120 pmol/min per mg of protein and apparent Km values of 220 microM with both substrates. In addition to suggesting that the recognition of the substrate by the adenylate cyclase may not require a specific chemical structure of the 5-membered ring of the base or a unique configuration about either the glycosyl or the C(5')-C(4') bond, the results of this study are consistent with the idea that the cytotoxicity observed with the adenosine analog formycin may be the result of its metabolism to cFoMP. Furthermore, these studies indicate that the fluorescent analog FoTP can be used, in combination with HPLC, to provide an alternative, nonradioactive direct method for the assay of adenylate cyclase catalytic activity.
Matrix protein in planar membranes: clusters of channels in a native environment and their functional reassembly.
Authors: Schindler H , Rosenbusch J P
Published: May 2006

Planar bilayers formed from Escherichia coli outer membrane vesicles exhibit conductance properties similar to those previously observed in bilayers reconstituted from aggregates of matrix protein, the major outer membrane protein. Discrete conductance steps are observed, reflecting voltage-dependent transmembrane channels. These exist in clusters which are activated by voltage. After activation, channels close with increasing potentials and reopen reversibly at lower voltage. Depending on the sign of the potential, two distinct closed states of the pores are observed. Cooperative interactions, hysteresis effects, relaxation times, and values of channel conductance depend on cluster size. These properties provide the reference data for the reconstitution of membrane function from individual components. Planar bilayers were formed from vesicles containing either solubilized matrix protein in a homogeneous trimeric state or bacterial glycolipid (lipopolysaccharide), or both. Activation of channel conductance required the presence of glycolipid and the formation of channel clusters, leading to conductance properties of the channels closely resembling those observed in native outer membranes. At very low concentrations of trimers, irreversible association to clusters by lateral diffusion was observed. Nearly quantitative recoveries of channels allowed the assignment of three pores per trimer.
Ultraviolet light action spectra for neoplastic transformation and lethality of Syrian hamster embryo cells correlate with spectrum for pyrimidine dimer formation in cellular DNA.
Authors: Doniger J , Jacobson E D , Krell K , DiPaolo J A
Published: May 2006

Action spectra were determined for neoplastic transformation, production of pyrimidine dimers, and lethality in Syrian hamster embryo cells. Of wavelengths between 240 and 313 nm, the most effective were 265 and 270. The relative sensitivities per quantum for transformation, pyrimidine dimer production, and lethality were essentially the same at each of the wavelengths tested. This action spectrum for transformation, which is relevant to carcinogenesis, is similar to spectra obtained previously by measuring other cellular responses in either microbial or mammalian systems. Because the action spectra for cytotoxicity and transformation are the same as the spectrum for dimer production, DNA is suggested as the target for all these processes.
Interleukin 2 is mitogenic for nu/nu and nu/+ murine spleen cells.
Authors: Lipsick J S , Kaplan N O
Published: May 2006

Interleukin 2 (IL-2), a product of activated T lymphocytes but not of T-cell-deficient spleen cells of congenitally athymic (nu/nu) mice, is shown to be strongly mitogenic for spleen cells from both nu/nu and nu/+ mice in the absence of serum. This response does not depend on the presence of additional mitogen or antigen as has been previously reported and is dose dependent with respect to IL-2. Plots of the logarithm of cell number versus logarithm of response indicate that IL-2-induced mitogenesis of nu/nu spleen cells is a one-cell event (slope = 1.28 +/- 0.21, mean +/- SD), whereas the response of nu/+ spleen cells to concanavalin A is a three-cell event (slope = 3.18 +/- 0.16). The nu/nu spleen cells proliferating in response to IL-2 are at least 80% T lymphocytes by the third day of culture, as demontrated by lysis with monoclonal anti-Thy-1 antibody and complement. These results suggest that one of the major roles of the thymus may be to induce IL-2 production in a subpopulation of lymphocytes that is then persistent.
Breakage and propagation of the stony coral
Acropora cervicornis
Authors: Tunnicliffe Verena
Published: May 2006

Populations of the staghorn coral,
Acropora cervicornis
, often form dense monotypic stands on shallow Caribbean reefs. This coral species has a fragile structure that results in large numbers of broken branches and toppled colonies, especially in high wave activity. Although more than 80% of the corals in the studied population were broken from their bases, most had become reanchored to regrow rapidly. There is little evidence of sexual reproduction, and it appears that this coral has come to dominate much of the Jamaican reef community by propagation through fragmentation.
Effect of agents that produce membrane disorder on lysis of erythrocytes by complement.
Authors: Shin M L , Hänsch G , Mayer M M
Published: May 2006

To evaluate the effect of membrane lipid acyl-chain packing on the efficiency of cell lysis by complement, we have studied membrane modulation by 2-(2-methoxy)-ethoxyethyl-8-(cis-2-n-octylcyclopropyl)-octanoate (A2C) and by myristoleyl alcohol, the cis isomer of a C14:1 aliphatic alcohol. These substances are known to increase the membrane lipid disorder by virtue of the bend in their acyl chains, which is believed to loosen the phospholipid acyl-chain packing. We have found that both of these compounds markedly enhance the lysis of erythrocytes by the terminal complement proteins C5b-9. The enhancing effect by A2C is operative in the formation of erythrocytes carrying complement components C5b, C6, and C7, as well as in the subsequent reactions with complement components C8 and C9. We have also found that A2C-treated erythrocytes bind C5b6 to a measurable extent, whereas untreated erythrocytes do not. We attribute this to a shift in the partition equilibrium of C5b6 toward membrane association, which would improve lytic efficiency. The increase of membrane lipid disorder by these agents would also be expected to increase insertion of hydrophobic peptides from C7, C8, and C9, with consequent gain in lytic efficiency. Treatment of erythrocytes with sublytic doses of NaDodSO4, or Triton X-100 did not enhance lysis by C5b-9 appreciably, suggesting that enhancement of lysis by C5b-9 is not a general property of amphiphiles.
Antigen-induced in vitro antibody production in humans: a model for B cell activation and immunoregulation.
Authors: Volkman D J , Lane H C , Fauci A S
Published: May 2006

The precise events associated with B cell activation in humans are a subject of intense investigation. It has been difficult to develop an in vitro model of antigen-specific triggering of antibody synthesis by human peripheral blood mononuclear cells that is independent of exogenous mitogens. In the present study a sensitive and reproducible culture system and enzyme-linked immunosorbent assay have been established wherein antigen alone is used to trigger antigen-specific antibody synthesis by mononuclear cells from subjects immunized to keyhole limpet hemocyanin (KLH). The in vitro antigen-induced anti-KLH response is comparable in magnitude to that induced by pokeweed mitogen, is predominantly IgM in isotype, and is accompanied by a simultaneous increase in polyclonal antibody production. Anti-KLH responses were seen at in vitro KLH concentrations as low as 0.05 microgram/ml. However, concentrations of KLH greater than 5 microgram/ml resulted in profound suppression of the anti-LHL response while continuing to trigger large amounts of total polyclonal immunoglobulin synthesis. This suppression by high concentrations of antigen was also observed in pokeweed mitogen-driven anti-KLH production. These observations are consistent with previous results from the mouse model showing a close association between antigen-specific and polyclonal responses and the phenomenon of antigen-induced, antigen-specific suppression. Thus, an in vitro model of antigen induction of antigen-specific antibody synthesis in human peripheral blood mononuclear cells has been demontrated and should prove useful in exploring the mechanism of human B cell activation and immunoregulation.
Herpes simplex virus (type 1) thymidine kinase gene does not transform cells morphologically.
Authors: Hampar B , Derge J G , Boyd A L , Tainsky M A , Showalter S D
Published: May 2006

BALB/c-derived 10E2 cells were made thymidine kinase(TK)-negative and one isolated clone (B2) was used for studying morphological and biochemical transformations by herpes simplex virus (HSV) type 1 (strain 10412). The B2 cells displayed a "normal" flat appearance and were nontumorigenic in nude mice when tested at frequent intervals over a period of 45 subcultures. B2 cells infected with UV-irradiated HSV (UV-HSV) and maintained in normal growth medium showed foci of spindle-shaped cells after one subculture. The cells from these morphologically transformed foci were tumorigenic in nude mice and were TK negative. B2 cells infected with UV-HSV or transfected with the HSV-1 TK gene and maintained in TK-selective medium showed discrete colonies of cells which displayed a normal flat appearance and expressed the viral TK enzyme. These biochemically transformed B2 cells were nontumorigenic in nude mice. The findings with B2 cells indicate that biochemical and morphological transformations by HSV-1 are independent events and suggest that the HSV-1 TK gene is a suitable vehicle for introducing non-TK genes into cells to assess their transforming potential.
Solid-phase peptide synthesis under continuous-flow conditions.
Authors: Lukas T J , Prystowsky M B , Erickson B W
Published: May 2006

A system is described for solid-phase synthesis of peptides under continuous-flow conditions with liquid chromatographic equipment, conventional polystyrene supports, and well-defined chemistry. The model tetrapeptide Leu-Ala-Gly-Val was assembled in 99.3% purity in about 4 hr on microporous copoly(styrene-1% divinylbenzene). During coupling, the preformed symmetric anhydrides were conserved by being recycled. Relative yields of the peptide products were determined quantitatively in 20 min by reverse-phase high-pressure liquid chromatography. This rapid assay system was used to examine the influence on product yields of (i) the time and number of couplings per cycle, (ii) microporous versus macroporous polystyrene, and (iii) tert-butoxycarbonyl (Boc) group versus 9-fluorenylmethoxycarbonyl for amine protection. Use of microporous polystyrene and two 30-min couplings of Boc-amino acids per cycle gave the best results. This continuous-flow system provides a rapid and efficient approach to solid-phase peptide synthesis. A 17-residue peptide from chicken ovalbumin was obtained in similar purity and yield from a discontinuous synthesis and from a continuous-flow synthesis.
Anti-Rho(D) IgG binds to band 3 glycoprotein of the human erythrocyte membrane.
Authors: Victoria E J , Mahan L C , Masouredis S P
Published: May 2006

Alkali-extracted erythrocyte ghost membranes from Rho(D)-positive and Rho(D)-negative donors were incubated with human immune anti-Rho(D) IgG and nonimmune IgG. After sensitization with IgG, the integral membrane proteins were solubilized in Brij 36T nonionic detergent and chromatographed by gel filtration. There was a distinct resolution of IgG into free and membrane-complexed forms. The IgG-complexed membrane proteins were isolated by the use of a staphylococcal protein A affinity support. The protein A-bound complexes were examined for polypeptide composition by gel electrophoresis after elution. Only Rho(D)-positive membrane proteins incubated with immune anti-Rho(D) IgG revealed intact band 3. Control Rh-negative membrane proteins that had reacted with immune anti-Rho(D) IgG and the Rh-positive membranes that had reacted with nonimmune IgG showed only low molecular weight fragments of band 3 that bound nonspecifically to IgG. Arguments are presented supporting a band 3 localization for the Rh antigen.
Eukaryotic translational control: adeno-associated virus protein synthesis is affected by a mutation in the adenovirus DNA-binding protein.
Authors: Jay F T , Laughlin C A , Carter B J
Published: May 2006

Growth of adeno-associated virus (AAV) requires expression of certain adenovirus (Ad) genes in the same cell. AAV particles contain three proteins, VP1 (Mr 85,700), VP2 (Mr 72,000), and VP3 (Mr 61,500). These proteins have overlapping peptide maps. We recently reported that AAV RNAs make up a 3'-coterminal family of overlapping molecules. We report here that the most abundant AAV mRNA, a 2.3-kilobase spliced RNA, codes for all three proteins--VP1, VP2, and VP3--when translated in an in vitro reticulocyte lysate. This shows that the AAV capsid proteins are coded by the genome sequence between map positions 48.0 and 96.0 (1 map unit is 1% of the genome or 47 base pairs). When AAV was grown in human KB cells with the Ad temperature-sensitive mutant Ad5ts125 at the nonpermissive temperature (40 degrees C), the accumulation in vivo of AAV capsid proteins VP1, VP2, and VP3 was decreased to less than 1/50th. However, normal amounts of the 2.3-kilobase mRNA were accumulated, and this RNA could be efficiently translated in an in vitro reticulocyte lysate system to yield VP1, VP2, and VP3. These experiments suggest that in infected cells control is exerted upon the AAV 2.3-kilobase mRNA at the translational level and that this control can be influenced by mutations in Ad. These Ad mutations map in the region 2 early gene for the Ad DNA-binding protein. The temperature-sensitive system that we have studied may be useful for analysis of translational control of a eukaryotic mRNA.
Location of platinum binding sites on bacteriorhodopsin by electron diffraction
Authors: Dumont Mark E. , Wiggins J. W. , Hayward S. B.
Published: May 2006

A platinum-containing derivative of bacteriorhodopsin has been prepared by treating purple membranes with glycyl-L-methionatoplatinum. Low-dose electron diffraction was used to identify Pt binding sites in the 5.6 Å resolution reconstruction of the bacteriorhodopsin unit cell in projection. This is a necessary first step in the use of the Pt derivative for identifying the parts of the amino acid sequence corresponding to the α helices in the bacteriorhodopsin structure and for obtaining phases for reflections out to 3.5 Å resolution by the method of heavy-atom isomorphous replacement. The largest peak in a Fourier difference map between platinum-labeled and native purple membrane is larger than the spurious features expected to arise from errors in measurements of diffraction intensities.
Adrenocorticotropin-like and alpha-melanotropin-like peptides in a subpopulation of human gastrin cell granules: bioassay, immunoassay, and immunocytochemical evidence.
Authors: Larsson L I
Published: May 2006

Adrenocorticotropin (ACTH)-like and alpha-melanotropin (alpha-MSH)-like peptides have been localized to a subpopulation of cytoplasmic (secretory) granules of human antropyloric gastric cells and of fetal and neoplastic gastrin cells. These granules also store gastrin and belong to the electron-dense variety of gastrin cell granules. Gastrin cells also contain granules of low to medium electron density; these store only gastrin and do not react with ACTH or alpha-MSH antisera. The alpha-MSH immunoreactive peptide was shown also to display alpha-MSH bioactivity by a combined immunosorbent-bioassay technique. This peptide cochromatographs with synthetic alpha-MSH in several systems and is not detected in oxyntic mucosa or in gastric muscle wall. As in the pituitary intermediate lobe, the alpha-MSH-like peptide may be formed by cleavage of ACTH-like peptides also in gastrin cells. These data provide additional evidence for local formation of ACTH/alpha-MSH-related peptides in gastrin cells and suggest a heterogenous peptide make-up of endocrine cell granules.
High molecular weight microtubule-associated proteins are preferentially associated with dendritic microtubules in brain.
Authors: Matus A , Bernhardt R , Hugh-Jones T
Published: May 2006

The distributions of tubulin and high molecular weight microtubule-associated proteins (HMWPs) in brain were determined by immunoperoxidase histochemistry with specific antisera. Tubulin was found in microtubules of both neurons and glia and both axons and dendrites. HMWPs were found only in neurons where, in all cases examined, they were associated with dendritic microtubules but not those in axons. Both tubulin and HMWPs were also found in postsynaptic densities. These results indicate that brain microtubules vary in chemical composition. The preferential association of HMWPs with dendritic microtubules suggests that they may play a role in distinguishing between dendritic and axonal export routes from the cell body.
Aortic smooth muscle cells contain vimentin instead of desmin.
Authors: Frank E D , Warren L
Published: May 2006

The 10-nm filament subunit proteins of smooth muscle cells in the mammalian aorta were analyzed by immunofluorescence and by two-dimensional gel electrophoresis. Indirect immunofluorescence studies on frozen sections of aorta showed intense staining of the tunica media by antibodies to vimentin, whereas no reaction could be detected with antibodies to desmin. Crude preparations from the tunica media contain a protein with molecular weight and isoelectric point similar to those of vimentin. Desmin was not detected on these same two-dimensional gels. We conclude that aortic smooth muscle cells contain vimentin as the predominant form of 10-nm filament protein subunit, unlike other muscle cells in which desmin predominates. Other immunofluorescence results indicate that the aorta may differ from smaller blood vessels which appear to contain both desmin and vimentin.
Intracellular localization of DNA polymerase alpha.
Authors: Brown M , Bollum F J , Chang L M
Published: May 2006

Immunoglobulin (IgG) and the F(ab')2 fragment of IgG were prepared from serum of a rabbit immunized with purified calf thymus DNA polymerase alpha (deoxynucleosidetriphosphate:DNA deoxynucleotidyltransferase, EC 2.7.7.7). An indirect immunofluorescent method based on these reagents was used to detect the intracellular localization of DNA polymerase alpha in primary fetal bovine fibroblasts. The results show that the bulk of DNA polymerase alpha is located in the perinuclear region of the cytoplasm. Immunofluorescent staining of cytoplast and Ficoll-Paque gradient-purified karyoplast fragments resulting from cytochalasin enucleation show the presence of DNA polymerase alpha in cytoplasts and the virtual absence of the enzyme in the nucleus of the karyoplast itself. The implication of this unusual intracellular location for DNA polymerase alpha is discussed.
Monoclonal antibodies to the thyrotropin receptor: implications for receptor structure and the action of autoantibodies in Graves disease.
Authors: Yavin E , Yavin Z , Schneider M D , Kohn L D
Published: May 2006

Hybridoma cells have been obtained by fusing P3-NS1/1-Ag4-1 mouse myeloma cells with spleen cells from mice immunized with solubilized preparations of the thyrotropin receptor. Five clones were produced that secrete a monoclonal antibody whose binding to thyroid membranes is specifically inhibited by unlabeled thyrotropin. The antibody interacts with functioning thyroid cells in culture but not with nonfunctioning cells; this interaction is prevented by thyrotropin. The antibodies are capable of competitively blocking thyrotropin binding to bovine thyroid membrane preparations; they prevent 125I-labeled thyrotropin binding to a solubilized preparation of the glycoprotein component of the bovine thyrotropin receptor but are unable to inhibit 125I-labeled thyrotropin binding to liposomes containing gangliosides at comparable concentrations. They prevent 125I-labeled thyrotropin binding to rat, bovine, or human (Graves disease) thyroid membrane preparations. They do not stimulate adenylate cyclase activity in thyroid membrane preparations but can inhibit thyrotropin-stimulated iodide uptake by functioning thyroid cells in culture.
Deposition of plasma fibronectin in tissues.
Authors: Oh E , Pierschbacher M , Ruoslahti E
Published: May 2006

Tissue distribution of human fibronectin injected intravenously into mice was studied by using immunofluorescence with species-specific antisera to human and mouse fibronectins. Human fibronectin was detected in the tissues of mice injected with human fibronectin. The distribution of the injected fibronectin was indistinguishable from that of mouse fibronectin. The staining for human fibronectin in the livers of injected mice was unaffected by perfusion of the livers prior to the preparation of tissue sections, and human IgG injected in mice as a control was not detectable in tissues by immunofluorescence. Mice were also injected with fragments of fibronectin with molecular weights close to 200,000. These fragments lack parts of the NH2 and COOH termini of the fibronectin polypeptide, including the part with the interchain disulfide bond(s), but retain the ability to bind to collagen and heparin and the ability to mediate cell attachment. They showed essentially no tissue incorporation, suggesting that the integrity of the fibronectin molecule is important for the accumulation of fibronectin in tissues. The incorporation of injected fibronectin into tissues demonstrated here suggests that circulating fibronectin contributes to the extracellular matrix of tissues.
Random walks with self-similar clusters
Authors: Hughes Barry D. , Shlesinger Michael F. , Montroll Elliott W.
Published: May 2006

We construct a random walk on a lattice having a hierarchy of self-similar clusters built into the distribution function of allowed jumps. The random walk is a discrete analog of a Lévy flight and coincides with the Lévy flight in the continum limit. The Fourier transform of the jump distribution function is the continuous nondifferentiable function of Weierstrass. We show that, for cluster formation, it is necessary that the mean-squared displacement per jump be infinite and that the random walk be transient. We interpret our random walk as having an effective dimension higher than the spatial dimension available to the walker. The difference in dimensions is related to the fractal (Hausdorff-Besicovitch) dimension of the self-similar clusters.
Interaction of tubulin with ribose-modified analogs of GTP and GDP: evidence for two mutually exclusive exchangeable nucleotide binding sites.
Authors: Hamel E , Lin C M
Published: May 2006

Interactions of tubulin with a number of guanine nucleotides modified at the 2' and 3' ribose hydroxyls were examined. Deoxy analogs of GTP were equal or superior to GTP in supporting tubulin polymerization, but analogs bearing either methyl or phosphate groups on the hydroxyls had significantly reduced ability to support polymerization. These substituted GTP analogs were hydrolyzed at the 5'-gamma-phosphate position, although less rapidly than GTP, at rates exceeding those of polymerization. GTP hydrolysis, however, was closely coupled to polymerization. Moreover, the partially active GTP analogs were not effective inhibitors of GTP-dependent polymerization. These data indicate that the substituted GTP analogs have reduced affinity for tubulin at the exchangeable site because of steric factors. No deoxy or substituted GDP analog was as effective as GDP itself in inhibiting GTP-supported tubulin polymerization. Furthermore, there was no apparent relationship between the ability of nucleoside 5'-triphosphates to support polymerization and that of nucleoside 5'-diphosphates to inhibit the reaction. These findings suggest that GTP and GDP may actually bind to different, mutually exclusive sites rather than to a single exchangeable site.
On the mechanism of retrovirus-induced avian lymphoid leukosis: deletion and integration of the proviruses.
Authors: Fung Y K , Fadly A M , Crittenden L B , Kung H J
Published: May 2006

There is considerable evidence that infection by avian lymphoid leukosis viruses can led to tumor development in the target organ of the host. The mechanism by which virus-induced oncogenic transformation occurs, however, is not clearly understood. As a first step toward deciphering this process, we have characterized the proviruses of the lymphoid leukosis viruses in DNAs extracted from the leukotic and metastatic tumors by using restriction enzyme digestion and filter hybridization analysis with radioactive probes specific for the infecting genome. Our results indicate (i) that lymphoid leukosis tumors are clonal in origin; (ii) that there are multiple sites in the cellular genome of the target tissue where the virus DNA can integrate and that, in the majority of the tumors, at least one such site of each tumor is adjacent to a cellular sequence related to the oncogene of MC-29 virus; and (iii) that deletions and other structural alterations in the proviral DNA may facilitate tumorigenesis.
Repair of DNA double-strand breaks in Escherichia coli cells requires synthesis of proteins that can be induced by UV light.
Authors: Krasin F , Hutchinson F
Published: May 2006

The repair of DNA double-strand breaks in Escherichia coli cells irradiated with gamma rays occurs only after new proteins are synthesized in response to damage introduced in the genome DNA. One protein whose synthesis is thus induced is the recA protein, and previous work has shown that recA- cells do not repair double-strand breaks. However, inducing recA protein by treating cells with nalidixic acid does not induce repair of double-strand breaks, so this repair requires more than the presence of the recA protein. When repair of double-strand breaks is blocked, the genome DNA is degraded by an endonuclease-like action. Evidence is presented to show that the inducible inhibition of DNA degradation after x-irradiation [Pollard, E. C. & Randall, E. P. (1973) Radiat. Res. 55, 265] is probably caused by the inducible repair of DNA double-strand breaks.
Cloning a cDNA for the pro-alpha 2 chain of human type I collagen.
Authors: Myers J C , Chu M L , Faro S H , Clark W J , Prockop D J , Ramirez F
Published: May 2006

Poly(A)-RNA enriched for type I procollagen sequences was isolated from normal human fibroblasts and used as template to synthesize double-stranded cDNA with avian myeloblastosis virus (AMV) reverse transcriptase. After the ends had been blunted with nuclease S1 and dGMP tails had been added with terminal deoxynucleotidyltransferase, the double-stranded cDNA was annealed with pBR322 DNA that had previously been cleaved with EcoRI, blunted with AMV reverse transcriptase, and dCMP-tailed with terminal deoxynucleotidyltransferase. The chimeric molecule was used to transform Escherichia coli strain HB101. Ninety-five recombinant clones were obtained and screened by dot hybridization analysis using 32P-labeled cDNA synthesized from the original poly(A)-RNA collagen-enriched population. Three positive clones were isolated and further characterized by blot hybridization techniques and by EcoRII digestion. One clone with an insert of 2.2 kilobases was shown to contain sequences encoding for the pro-alpha 2 chain of human type I procollagen. DNA sequence analysis of a 172-nucleotide fragment demonstrated that the cloned cDNA extends from amino acid position 450 of the alpha 2 chain to the middle of the COOH-terminal propeptide.
Heat shock proteins are methylated in avian and mammalian cells.
Authors: Wang C , Gomer R H , Lazarides E
Published: May 2006

Exposure of chicken cells grown in tissue culture to heat shock or sodium arsenite results in a dramatic increase in the synthesis of three major polypeptides with molecular weights of 83,000 (HSP 83), 68,000 (HSP 68; referred to here as "thermin"), and 25,000 (HSP 25). Incubation of BHK-21 or HeLa cells under the same conditions results in induction of HSP 68 and a 66,000-dalton polypeptide (HSP 66). Chicken thermin is resolved by isoelectric focusing into a major acidic and a more-basic component; mammalian thermin is resolved only into one major acidic component. HSP 83 and the acidic form of thermin are highly conserved in all avian and mammalian cells examined as judged by their electrophoretic mobilities, isoelectric points, and one-dimensional peptide maps. In addition, the acidic form of thermin is indistinguishable from a protein that copurifies with brain microtubules and that remains associated with the intermediate filament-enriched Triton/KCl cytoskeletons of cells grown in tissue culture. Thermin is also a component of skeletal myofibrils. HSP 83 and thermin are methylated in cells cultured under normal growth conditions. Induction of heat shock proteins by incubation of cells in the presence of sodium arsenite results in a marked methylation of the newly synthesized thermin. Under the same experimental conditions, no significant increase in methylation of the HSP 83 is observed. HSP 25 is not methylated in untreated cells or in cells treated with sodium arsenite. These results suggest that methylation of heat shock proteins may have an important role in regulating their function.
Electron microscopy shows periodic structure in collagen fibril cross sections.
Authors: Hulmes D J , Jesior J C , Miller A , Berthet-Colominas C , Wolff C
Published: May 2006

X-ray diffraction was used to monitor the effects of electron microscope fixation, staining, and embedding procedures on the preservation of the three-dimensional crystalline order in collagen fibrils of rat tail tendon. A procedure is described in which the characteristic 3.8-nm lateral spacing is preserved, with increased contrast, in the diffraction pattern of the embedded fiber. This spacing is correlated with the separation between the tangentially oriented equally spaced lines of density observed in electron microscope ultrathin fibril cross sections of the same material. Optical diffraction of electron micrographs gives an objective measure of the periodicity and suggests that the fibril is composed of concentrically oriented crystalline domains. These observations, when combined with a recent interpretation of the native x-ray diffraction data [Hulmes, D. J. S. & Miller, A. (1979) Nature (London) 282, 878-880] suggest a tentative model for the three-dimensional structure of collagen fibrils.
Mutated beta-actin gene: coexpression with an unmutated allele in a chemically transformed human fibroblast cell line.
Authors: Hamada H , Leavitt J , Kakunaga T
Published: May 2006

By in vitro translation, we have identified the mRNA species that codes for a novel actin polypeptide (Ax-actin) in the chemically transformed human fibroblast line HuT-14. The relatedness of the coding sequences of the Ax- and beta-actin genes is indicated by our finding that pcDd actin ITL-I DNA, a recombinant plasmid DNA that contains a DNA sequence complementary to actin mRNA of Dictyostelium discoideum, hybridizes both the Ax-actin mRNA and the beta-actin mRNA but not the gamma-actin mRNA. In contrast, pcHa-1 DNA, a recombinant plasmid constructed by cloning a DNA sequence complementary to human actin mRNA from HuT-14 cells into pBR322, hybridized to all three mRNA species. In addition, no difference was observed between Ax- and beta-actin mRNAs when their molecular size was determined either by sucrose density gradient sedimentation or by methyl mercury agarose gel electrophoresis. Southern blot transfer of radioactive pcDd actin DNA to restriction endonuclease-digested Hut-14 DNA produced only a single hybrid band (a 6-kilobase fragment); the pcHa-1 DNA probe detected one additional band (a 3-kilobase fragment). These results suggest that HuT-14 cells contain only one copy per haploid genome for Ax- or beta-actin. When considered together with recent determination of the entire amino acid sequences of Ax- and beta-actin, our findings indicate that Ax-actin is the product of a mutated beta-actin gene and are evidence for the occurrence of a mutation in a chemically transformed cell.
Correlation of double-minute chromosomes with unstable multidrug cross-resistance in uptake mutants of neuroblastoma cells.
Authors: Baskin F , Rosenberg R N , Dev V
Published: May 2006

A series of increasingly drug-resistant cell populations were selected and cloned from C-46 murine neuroblastoma with the chemotherapeutic drugs maytansine, vincristine, adriamycin, or Baker's antifol. All clones demonstrated reciprocal cross-resistance to these structurally and functionally diverse drugs and failed to accumulate radiolabeled vincristine, colchicine, or Baker's antifol despite normal drug binding to cell homogenates. Initial isolates of drug-resistant populations were genetically unstable, rapidly reverting to a drug-sensitive phenotype when grown without drug, at 0.05 reversion per cell division. After prolonged growth in drug, this drug-resistant genotype stabilized. Mean chromosome number increased 300% in an initially isolated 20-fold maytansine-resistant clone, which also displayed numerous double-minute chromosomes. Descendants 240-fold more resistant than the parent, also unstable, possessed the wild-type complement of 80 chromosomes, but 45% of these cells possessed 24 double-minute chromosomes per cell; such chromosomes were absent from the drug-sensitive parental clone. Only 1.0 and 1.2 double-minute chromosomes per cell were seen in a 7-fold stably resistant revertant or 1200-fold stably resistant descendants, respectively. Double-minute chromosomes containing amplified genes for the drug target dihydrofolate reductase (tetrahydrofolate dehydrogenase; 5,6,7,8-tetrahydrofolate:NADP+ oxidoreductase, EC 1.5.1.3) have been reported in an unstable methotrexate-resistant R1-A sarcoma. These extrachromosomal gene copies were absent in stably resistant progeny. The presence of similar particles in unstably drug-resistant uptake mutants of neuroblastoma and their diminution in stably resistant descendants supports and extends their possible role in the rapid onset and instability of epigenetic drug resistance in cancer chemotherapy.
Attachment of smooth muscle cells to collagen and their migration toward platelet-derived growth factor.
Authors: Grotendorst G R , Seppä H E , Kleinman H K , Martin G R
Published: May 2006

Smooth muscle cells use fibronectin to bind to type I and type III collagens but bind to type V collagen by a trypsin-resistant intrinsic glycoconjugate. The binding site on type V collagen is located in the alpha A chain. By using collagen-coated filters in a modified Boyden chamber assay for chemotaxis, it was observed that the platelet-derived growth factor was chemotactic for smooth muscle cells but that several other growth factors were inactive. We suggest that the migration of smooth muscle cells from the media to the intima of a blood vessel, which leads to the formation of an atherosclerotic plaque, may be the result of a chemotactic migration of cells responsive to the platelet-derived growth factor.
On the possibility of metabolic control of replicon "misfiring": relationship to emergence of malignant phenotypes in mammalian cell lineages.
Authors: Varshavsky A
Published: May 2006

Constraints of a multireplicon chromosomal organization and of the necessity to maintain constant gene dosages demand that each origin of replication in a eukaryotic cell "fire" (initiate replication) only once per cell cycle. The central idea of this work is that a low probability of an extra ("illegitimate") round of DNA replication (called below "replicon misfiring") within any given chromosomal domain could be increased by certain substances of either intra- or extracellular origin. The term " "firone" is proposed for such a substance. It is shown that existence of firones could greatly speed up evolution of cellular systems under selection pressure, a developing tumor being one example of such a system. Experimentally testable predictions of the firone hypothesis are discussed.
Possible functions of mesenchyme cell-derived fibronectin during formation of basal lamina
Authors: Brownell Anna G. , Bessem Conny C. , Slavkin Harold C.
Published: May 2006

Epithelial synthesis and secretion of basal lamina has been considered to be a general feature of various vertebrate epithelium-mesenchyme interacting systems (e.g., salivary gland, mammary gland, feather, hair, and tooth morphogenesis). It has been repeatedly assumed that embryonic ectoderm and ectodermal derivatives, such as epithelial tissues associated with tooth morphogenesis, synthesize and secrete basal lamina. Basal lamina of embryonic mouse tooth organs contain laminin, type IV collagen, glycosaminoglycans, and possibly fibronectin. Ectodermally derived epithelia produce laminin, collagens, and glycosaminoglycans but they do not appear to produce fibronectin. Mesenchyme can effect basal lamina formation
in vitro
by releasing mesenchyme-derived fibronectin. Theiler stage 25 molar tooth mesenchymal and epithelial tissues were enzymatically separated and cultured in chemically defined media without serum, embryonic extracts, or antibiotics for periods not exceeding 24 hr. Isolated epithelia did not reconstitute a basal lamina. Mesenchymepreconditioned media, fibronectin substrata, or addition of 10% fetal calf serum induced reconstitution of epithelium-derived basal lamina. Dental mesenchyme-preconditioned medium contained, as a major component, a protein of

M
r

≈2.3 × 10
5
identified as fibronectin by the criteria of gelatin binding and subunit molecular weight. Fibronectin was not produced by isolated epithelia. These results support the hypothesis that basal lamina ultrastructural organization results from supramolecular interactions between epithelium-derived macromolecules (e.g., type IV collagen, proteoglycans, glycosaminoglycans, and laminin) with mesenchyme-derived cell surface fibronectin.
A novel type of T-T cell interaction removes the requirement for I-B region in the H-2 complex.
Authors: Baxevanis C N , Nagy Z A , Klein J
Published: May 2006

When tested in the in vitro T-cell proliferation assay, H-2a cells are nonresponders to lactate dehydrogenase B (LDH-B; L-lactate:NAD+ oxidoreductase, EC 1.1.1.27) and to IgG2a myeloma protein. However, the cells can be converted into responders either by the addition to the culture of monoclonal anti-Ia.m7 antibody or by the removal from the culture of Lyt-2+ [T-lymphocyte-associated alloantigen (Lyt)-2 positive] lymphocytes. In both instances, the responsiveness can be suppressed again by the addition to the culture of monoclonal antibodies to I region-associated (Ia) molecules controlled by the I-A subregion. These data suggest that, in some H-2 haplotypes, the response to LDH-B and IgG2a is the result of interaction between the I-A and I-E subregions. The H-2a haplotype carries a responder allele at the I-A subregion but the responsiveness of H-2a cells is normally suppressed by T cells recognizing the antigen in the context of the I-E molecules. When the recognition of I-E molecules is blocked by an antiserum or when the cells capable of this recognition are removed, the H-2a cells become responders. These experiments demonstrate a nonresponder turned responder by antibody inhibition. They also demonstrate that the postulate of the I-B subregion is no longer necessary and provide additional evidence that the Ia molecules are the products of the immune response (Ir) genes.
Expression of an antigen receptor on T cells does not require recombination at the immunoglobulin JH-C mu locus.
Authors: Cayre Y , Palladino M A , Marcu K B , Stavnezer J
Published: May 2006

Considerable evidence has accumulated suggesting that the antigen receptor(s) on T cells is coded for by genes for the variable (V) region of the immunoglobulin heavy (H) chains. In B cells, a complete gene for the immunoglobulin VH region is formed by somatic recombination of VH and joining region heavy chain (JH) gene segments [through an intermediate diversity(D) region gene segment]. In an attempt to determine whether a complete immunoglobulin VH region is expressed on T cells that bear an antigen receptor, we analyzed the restriction map of the JH-C mu locus in genomic DNA from two cloned murine cytotoxic T-lymphocyte (CTL) lines specific for the x-ray-induced leukemia RL male 1. We found no rearrangement of the JH C mu locus in the CTL lines, indicating that the T-cell antigen receptor(s) in these CTLs is not coded for by a complete immunoglobulin VH gene formed by joining of VH, (DH), and JH genes. In addition, we determined that C mu genes on both chromosomes were present and that there was no rearrangement of the C alpha, C kappa, or lambda chain genes in these CTL cells.