Showing papers by "Weizmann Institute of Science published in 1982"

Linear systems with delayed controls: A reduction

Abstract: Linear systems with delayed control action are transformed into systems without delays. Under an absolute continuity condition, the new system is an ordinary differential control equation. In the general case, the new system is a measure-differential control system. It is shown how the controllability, stabilization, and various optimization problems can be analyzed via the reduced systems.

Exact Critical Point and Critical Exponents of O ( n ) Models in Two Dimensions

Abstract: A two-dimensional $n$-component spin model with cubic or isotropic symmetry is mapped onto a solid-on-solid model. Subject to some plausible assumptions this leads to an analytic calculation of the critical point and some critical indices for $\ensuremath{-}2l~nl~2$.

Construction of Human Gene Libraries from Small Amounts cf Peripheral Blood: Analysis of β-Like Globin Genes

Abstract: We describe a rapid procedure for constructing cloned human genomic libraries from small amounts of peripheral blood High molecular weight DNA is isolated from 5–20 ml peripheral blood, partially cleaved with Eco R1, and 8–22 kb fragments are cloned using bacteriophage Charon 4A and a suitable Ecoli host Using this approach we have isolated and characterized several non-a globin clones from a Kurdish Jew with homozygous β thalassemia The ability to isolate suitable amounts of high molecular weight DNA from peripheral blood provides a relatively simple means of constructing human gene libraries representing a variety of hemoglobin disorders

Preferential effect of gamma interferon on the synthesis of HLA antigens and their mRNAs in human cells.

Abstract: Interferons produce a variety of biological effects on cells. They induce resistance to virus proliferation, inhibit cell growth, modify cell structure and differentiation, stimulate some immune functions and inhibit others. However, the different interferon (IFN) species may vary in their mechanism of action and, hence, in their relative efficiency for inducing each of the effect. IFN-gamma (type II) appears to show stronger immunoregulatory and growth inhibitory effects than antiviral effects, but this conclusion has been challenged in other reports. The aim of the present work is to compare the action of IFN-gamma and other (type I) interferons on the induction of (2'-5') oligo(A) synthetase which is probably part of the antiviral response and the induction of the histocompatibility HLA-A,-B,-C antigens. We have shown previously that the induction of both proteins is regulated by interferons at the mRNA level, but show here that IFN-gamma from stimulated human lymphocytes and from monkey cells transfected by cloned human IFN-gamma cDNA induced the HLA-A,-B,-C and beta 2-microglobulin mRNAs or proteins at concentrations over 100 times lower than those needed to induce the (2'-5')oligo(A) synthetase and the antiviral state. This difference was not found with IFN-alpha and -beta (type I).

Accumulation of beta-carotene in halotolerant algae: purification and characterization of beta-carotene-rich globules from Dunaliella bardawil (Chlorophyceae) [Algae].

Abstract: Dunaliella bardawil Ben-Amotz & Avron, but not most other Dunaliella species, has a unique property of being able to accumulate, in addition to glycerol, large amounts of β-carotene when cultivated under appropriate conditions. These include high light intensity, a high sodium chloride concentration, nitrate deficiency and extreme temperatures. Under conditions of maximal carotene accumulation D. bardawil contains at least 8% of its dry weight as β-carotene while D. salina grown under similar conditions contains only about 0.3%. Electron micrographs of D. bardawil grown under conditions of high β-carotene accumulation show many β-carotene containing globules located in the interthylakoid spaces of the chloroplast. The same algae grown under conditions where β-carotene does not accumulate, contain few to no β-carotene globules. The β-carotene-rich globules were released from the algae into an aqueous medium by a two-stage osmotic shock technique and further purified by centrifugal ion on 10% sucrose. The isolated purified globules were shown by electron microscopy to be free of significant contamination and composed of membrane-free osmiophilic droplets with an average diameter of 150 nm. Reversed phase high performance liquid chromatography of a total pigment extract of the cells revealed the presence of β-carotene as the major pigment, together with chlorophylls a and b, α-carotene and the xanthophylls lutein, neoxauthin and zeaxanthin. β-Carotene accounted for essentially all the pigment in the purified globules. Analysis of the algal and globule β-carotene fractions by HPLC showed that the β-carotene was composed of approximately equal amounts of all-trans β-carotene and of its 9-cis isomer. Intact D. bardawil cells contained on a dry weight basis about 30% glycerol, 30% protein, 18% lipid, 11% carbohydrate, 9%β-carotene and 1% chlorophyll. The β-carotene globules were composed of practically only neutral lipids, more than half of which was β-carotene. It is suggested that the β-carotene globules may serve to protect D. bardawil against injury by the high intensity irradiation to which this alga is usually exposed in nature.

How to reuse a “write-once≓ memory*

Abstract: Storage media such as digital optical disks, PROMS, or paper tape consist of a number of “write-once≓ bit positions (wits); each wit initially contains a “0≓ that may later be irreversibly overwritten with a “1.≓ It is demonstrated that such “write-once memories≓ (woms) can be “rewritten≓ to a surprising degree. For example, only 3 wits suffice to represent any 2-bit value in a way that can later be updated to represent any other 2-bit value. For large k, 1.29… · k wits suffice to represent a k-bit value in a way that can be similarly updated. Most surprising, allowing t writes of a k-bit value requires only t + o(t) wits, for any fixed k. For fixed t, approximately k · t/log(t) wits are required as k → ∞. An n-wit WOM is shown to have a “capacity≓ (i.e., k · t when writing a k-bit value t times) of up to n · log(n) bits.

Quantitative feedback theory

Abstract: In quantitative feedback theory, plant parameter and disturbance uncertainty are the reasons for using feedback. They are defined by means of a set Q = {P} of plant operators and a set D = {D} of disturbances. The desired system performance is defined by sets of acceptable outputs A u in response to an input u, to be achieved for all Pϵ Q. If any design freedom remains in the achievement of the design specifications, it is used to minimise the effect of sensor noise at the plant input. Rigorous, exact quantitative synthesis theories have been established to a fair extent for highly uncertain linear, nonlinear and time-varying single-input single-output, single-loop and some multiple-loop structures; also for multiple-input multiple-output plants with output feedback and with internal variable feedback, both linear and nonlinear. There have been many design examples vindicating the theory. Frequency-response methods have been found to be especially useful and transparent, enabling the designer to see the trade-off between conflicting design factors. The key tool in dealing with uncertain nonlinear and multiple-input multiple-output plants is their conversion into equivalent uncertain linear time-invariant single-input single-output plants. Schauder's fixed-point theorem justifies the equivalence. Modern control theory, in particular singular-value theory, is examined and judged to be comparatively inadequate for dealing with plant parameter uncertainties.

Visualization of the spread of electrical activity in rat hippocampal slices by voltage-sensitive optical probes.

Abstract: 1. Voltage-sensitive membrane-bound dyes and a matrix of 100 photodetectors were used to detect the spread of evoked electrical activity at the CA1 region of rat hippocampus slices. A display processor was designed in order to visualize the spread of electrical activity in slow motion.2. The stimulation of the Schaffer collateral-commissural path in the stratum radiatum evoked short latency (2-4 msec) fast optical signals, followed by longer latency (4-15 msec) slow signals which decayed within 20-50 msec. Multiple fast signals were frequently detected at the stratum pyramidale; they propagated toward the stratum oriens with an approximate conduction velocity of 0.1 m/sec.3. The fast signals were unaltered in a low Ca(2+) high Mg(2+) medium but were blocked by tetrodotoxin. These signals probably represent action potentials in the Schaffer collateral axons. Their conduction velocity was about 0.2 m/sec and their refractory period about 3-4 msec.4. The slow signals were absent in a low Ca(2+) medium and probably represent excitatory post-synaptic potentials (e.p.s.p.s) generated in the apical dendrites of the pyramidal cells. They were generated in the stratum radiatum, where the presynaptic signals were seen, and spread into somata and basal dendrites (the stratum pyramidale and oriens, respectively).5. The timing of the signals with fast rise-time, which were detected at the statum pyramidale, approximately coincided with the timing of the extracellularly recorded field potentials. These multiple discharges probably represent action potentials of the pyramidal cells. They spread back into the apical dendrites but with significant attenuation of the amplitudes of the high frequency components of the pyramidal action potentials.6. Hyperpolarizing potentials could be detected when strong stimuli were applied to the stratum radiatum or alveus. The net hyperpolarizations were detected only in the stratum pyramidale and the border region between the stratum pyramidale and radiatum. Frequently the inhibition was masked by the large e.p.s.p.s. However, its existence could be demonstrated by treatment of the slice with picrotoxin or a low Cl(-) medium. Under these conditions a long-lasting depolarization of the apical dedrites was evoked by the stimulation. This was associated with an increase of the multiple discharges in the stratum pyramidale and oriens.7. These studies illustrate the usefulness of voltage-sensitive dyes in the analysis of passive and active electrical properties, pharmacological properties and synaptic connexions in mammalian brain slices, at the level both of small neuronal elements (dendrites, axons) and of synchronously active neuronal populations.

A polynomial time algorithm for breaking the basic Merkle-Hellman cryptosystem

Abstract: The cryptographic security of the Merkle-Hellman cryptosystem has been a major open problem since 1976. In this paper we show that the basic variant of this cryptosystem, in which the elements of the public key are modular multiples of a superincreasing sequence, is breakable in polynomial time.

Activation of a cellular oncogene by DNA rearrangement: possible involvement of an IS-like element.

Abstract: Activation of a cellular oncogene by DNA rearrangement: possible involvement of an IS-like element

Purification and properties of a D-galactose/N-acetyl-D-galactosamine-specific lectin from Erythrina cristagalli

Abstract: The lectin from the seeds of Erythrina cristagalli has been isolated in high yield (75 %) and homogeneous form by affinity chromatography on a column of D-galactose-derivatised Sepharose. It is a glycoprotein with a molecular weight of 56800±900 and s20.w, = 3.9 S, composed of two subunits (apparent molecular weights of 28000 and 26000 respectively) both of which are glycosylated. The total carbohydrate content is 4.5% and it is comprised of mannose, N-acetylglucosamine, fucose and xylose in amounts corresponding to 7, 4, 2 and 2 mo1/56800 Da respectively. The amino acid composition of the lectin is characterised by a high content of acidic and hydroxy amino acids, low content of methionine and absence of cysteine. Valine is the only N-terminal amino acid detected. The lectin is a metalloprotein in that it contains 0.093% Mn and 0.13percnt; Ca (1 mol and 1.9 mo1/56 800 Da respectively), both of which are tightly bound to the protein. E. cristagalli lectin agglutinates untreated human erythrocytes of all blood types, as well as rabbit erythrocytes, at a concentration of 5-10 μg/ml. It is mitogenic for human peripheral blood T lymphocytes at an optimal concentration of about 100 pμg/ml, but is not mitogenic for mouse thymocytes or splenocytes. d-GahtOSe and various d-galactosides inhibit the hemagglutinating activity of the lectin. N-Acetyllactosarnine is most potent, completely inhibiting four agglutinating units of the lectin at 0.4 mM concentration. Lactose, N-acetyl-d-galactosamine and d-galactose are 5, 16 and 35 times less active respectively. Lactose specifically perturbs the ultraviolet spectrum of the lectin in the aromatic region. The difference spectrum obtained upon binding of the disaccharide to the lectin shows maxima at 291 nni and 282-284 nm, indicating a change in the environment of tryptophan residues of the protein upon binding of sugar.

Resolution of conglomerates by stereoselective habit modifications

Abstract: A method for resolution of conglomerates, based on morphological differences between the enantiomorphic crystals induced by tailor-made resolved impurities is described. The relationship between the crystal structure of the affected enantiomorph and the stereochemistry of the added impurity is analysed in the systems glutamic acid. HCl, asparagine. H2O and threonine in the presence of L- or D-amino acids, and it is found that the additive binds stereoselectively at the surface of the enantiomer of the same absolute configuration, occupying the same site of the amino acid groups of the host molecule. The modified side chains perturb in a second stage the regular growth of the crystal in the directions along which the side chains of the host are hydrogen bonded.

Nucleotide sequence of the rat skeletal muscle actin gene.

Abstract: The actins constitute a family of highly conserved proteins found in all eukaryotic cells. Their conservation through a very wide range of taxonomic groups and the existence of tissue-specific isoforms make the actin genes very interesting for the study of the evolution of genes and their controlling elements. On the basis of amino acid sequence data, at least six different mammalian actins have been identified (skeletal muscle, cardiac muscle, two smooth muscle actins and the cytoplasmic β- and γ-actins)1–5. Rat spleen DNA digested by the EcoRI restriction enzyme contains at least 12 different fragments with actin-like sequences but only one which hybridized, in very stringent conditions, with the skeletal muscle cloned cDNA probe6. Here we describe the sequence of the actin gene in that fragment. The nucleotide sequence codes for two amino acids, Met-Cys, preceding the known N-terminal Asp of the mature protein. There are five small introns in the coding region and a large intron in the 5′-untranslated region. Comparison of the structure of the rat skeletal muscle actin gene with the available data on actin genes from other organisms shows that while the sequenced actin genes from Drosophila and yeast have introns at different locations, introns located at codons specifying amino acids 41, 121, 204 and 267 have been preserved at least from the echinoderm to the vertebrates. A similar analysis has been done by Davidson7. An intron at codon 150 is common to a plant actin gene and the skeletal muscle acting gene.

Plant regeneration from Citrus protoplasts: Variability in methodological requirements among cultivars and species.

Abstract: Nucellar callus lines were established from two orange cultivars (‘Nucellar Shamouti’, ‘Shamouti Landau’), three mandarin cultivars (‘Murcott’, ‘Dancy’, ‘Ponkan’) one grapefruit cultivar (‘Duncan’) and sour orange (Citrus aurantium). These callus lines were initiated from in vitro cultured ovules of young fruits and maintained an embryogenic capacity. The plating efficiencies of protoplasts derived from these calli, as well as those of protoplasts from lemon (cv. ‘Villafranca’) nucellar callus were differentially affected by the maceration enzymes and by the sugars used as osmotic stabilizers. Plants with normal morphological features were regenerated from cultured protoplasts derived from each of the nucellar callus lines. The establishment of eight new protoplast systems in Citrus paves the way for cell genetics studies and for novel breeding approaches in these economically important orchard trees.

Autoantibodies to insulin receptor spontaneously develop as anti-idiotypes in mice immunized with insulin.

Abstract: Mice immunized with insulin developed antibodies to both insulin and the insulin receptor The antibodies to insulin receptor displaced labeled insulin from insulin receptors and mimicked the actions of insulin in stimulating the oxidation of glucose and its incorporation into lipids, and in inhibiting lipolysis The antibodies to insulin receptor could be blocked by or bound to the antibodies to insulin, and therefore were identified as anti-idiotypes Thus, immunization against a hormone may activate spontaneously an idiotype-anti-idiotype network resulting in antibodies to the hormone receptor

Effector T lymphocyte line cells migrate to the thymus and persist there

Abstract: The thymus gland has been known for some time to be the central organ of differentiation of T lymphocytes1,2. Stem cells migrate into the thymus from the bone marrow, differentiate and, as competent T lymphocytes, disperse from the thymus to the periphery, where contact with specific antigen induces immune reactivity2. The traffic of T lymphocytes between the thymus and periphery has been thought to be unidirectional and, unless the cells are leukaemic3 or the thymus gland has been irradiated4, re-entry of peripheral T lymphocytes has not been detected3. We now report that cells from lines of functionally active T lymphocytes reactive to self or foreign antigens can migrate back into the normal thymus gland and persist there for relatively long periods in a quiescent state until activated by contact with antigen. Hence, in addition to being the seat of T lymphocyte differentiation, the thymus is open to two-way traffic with the periphery and may function as a repository of immunological memory.

Lymphoid cell surface interaction structures detected using cytolysis-inhibiting monoclonal antibodies.

Abstract: We screened monoclonal antibodies obtained by xenogeneic immunization for their capacity to inhibit T cell-mediated cytolysis. These antibodies fell into two classes according to the cell structures they recognized, of 30-35 K and 94-180 K apparent molecular weight, respectively. The main features of these structures and of their interaction with the corresponding antibodies were reviewed. The inhibition of cytolysis by these antibodies was shown to occur mainly at the effector cell level, at the recognition stage of cytolysis, and to depend on the nature of target cells, effector cells, and link between these cells. T cell functions other than cytolysis were also inhibited by some of these antibodies. We considered various possible mechanisms to account for the inhibition of cytolysis by these mAb. We favor an hypothesis based on inhibition by these mAb of lymphoid cell surface interaction structures. This hypothesis was discussed within the general framework of cell interaction structures in immunological and non-immunological experimental systems.

Distribution of conformations and chain ends near the surface of a melt of linear flexible macromolecules

Abstract: In a melt of linear flexible macromolecules the conformations adopted by the chains follow the ideal Kuhn random walk distribution, because of the extremely high, but uniform, local conformational attrition factor. Long-range exclusion effects are overwhelmed and pseudoideal conditions prevail. One may assume that at an interface with a melt all but the uppermost segment layers are still ideal in the above sense. This assumption leads to a method allowing the enumeration of conformations according to their end-to-end distance and the determination of the mean square end-toend distance. The result is that coils in the interfacial layer tend to be compressed. The extent of the surface zone of altered end-to-end distribution is scaled by the root mean square end-to-end distance of the coils in the bulk of the melt.