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Showing papers in "Nature in 1990"


Journal ArticleDOI
11 Oct 1990-Nature
TL;DR: In this article, the authors demonstrate that poly(p-phenylene vinylene), prepared by way of a solution-processable precursor, can be used as the active element in a large-area light-emitting diode.
Abstract: CONJUGATED polymers are organic semiconductors, the semiconducting behaviour being associated with the π molecular orbitals delocalized along the polymer chain. Their main advantage over non-polymeric organic semiconductors is the possibility of processing the polymer to form useful and robust structures. The response of the system to electronic excitation is nonlinear—the injection of an electron and a hole on the conjugated chain can lead to a self-localized excited state which can then decay radiatively, suggesting the possibility of using these materials in electroluminescent devices. We demonstrate here that poly(p-phenylene vinylene), prepared by way of a solution-processable precursor, can be used as the active element in a large-area light-emitting diode. The combination of good structural properties of this polymer, its ease of fabrication, and light emission in the green–yellow part of the spectrum with reasonably high efficiency, suggest that the polymer can be used for the development of large-area light-emitting displays.

10,463 citations


Journal ArticleDOI
30 Aug 1990-Nature
TL;DR: Subpopulations of RNA molecules that bind specifically to a variety of organic dyes have been isolated from a population of random sequence RNA molecules.
Abstract: Subpopulations of RNA molecules that bind specifically to a variety of organic dyes have been isolated from a population of random sequence RNA molecules. Roughly one in 10(10) random sequence RNA molecules folds in such a way as to create a specific binding site for small ligands.

8,781 citations


Journal ArticleDOI
27 Sep 1990-Nature
TL;DR: In this article, a new form of pure, solid carbon has been synthesized consisting of a somewhat disordered hexagonal close packing of soccer-ball-shaped C60 molecules.
Abstract: A new form of pure, solid carbon has been synthesized consisting of a somewhat disordered hexagonal close packing of soccer-ball-shaped C60 molecules. Infrared spectra and X-ray diffraction studies of the molecular packing confirm that the molecules have the anticipated 'fullerene' structure. Mass spectroscopy shows that the C70 molecule is present at levels of a few per cent. The solid-state and molecular properties of C60 and its possible role in interstellar space can now be studied in detail.

6,650 citations


Journal ArticleDOI
02 Aug 1990-Nature
TL;DR: Three families of cell-surface molecules regulate the migration of lymphocytes and the interactions of activated cells during immune responses.
Abstract: The adhesive interactions of cells with other cells and with the extracellular matrix are crucial to all developmental processes, but have a central role in the functions of the immune system throughout life Three families of cell-surface molecules regulate the migration of lymphocytes and the interactions of activated cells during immune responses

6,595 citations


Journal ArticleDOI
31 May 1990-Nature
TL;DR: The amount and length of telomeric DNA in human fibroblasts does in fact decrease as a function of serial passage during ageing in vitro and possibly in vivo.
Abstract: The terminus of a DNA helix has been called its Achilles' heel. Thus to prevent possible incomplete replication and instability of the termini of linear DNA, eukaryotic chromosomes end in characteristic repetitive DNA sequences within specialized structures called telomeres. In immortal cells, loss of telomeric DNA due to degradation or incomplete replication is apparently balanced by telomere elongation, which may involve de novo synthesis of additional repeats by novel DNA polymerase called telomerase. Such a polymerase has been recently detected in HeLa cells. It has been proposed that the finite doubling capacity of normal mammalian cells is due to a loss of telomeric DNA and eventual deletion of essential sequences. In yeast, the est1 mutation causes gradual loss of telomeric DNA and eventual cell death mimicking senescence in higher eukaryotic cells. Here, we show that the amount and length of telomeric DNA in human fibroblasts does in fact decrease as a function of serial passage during ageing in vitro and possibly in vivo. It is not known whether this loss of DNA has a causal role in senescence.

5,454 citations


Journal ArticleDOI
01 Feb 1990-Nature
TL;DR: The mevalonate pathway produces isoprenoids that are vital for diverse cellular functions, ranging from cholesterol synthesis to growth control, and could be useful in treating certain forms of cancer as well as heart disease.
Abstract: The mevalonate pathway produces isoprenoids that are vital for diverse cellular functions, ranging from cholesterol synthesis to growth control. Several mechanisms for feedback regulation of low-density-lipoprotein receptors and of two enzymes involved in mevalonate biosynthesis ensure the production of sufficient mevalonate for several end-products. Manipulation of this regulatory system could be useful in treating certain forms of cancer as well as heart disease.

5,125 citations


Journal ArticleDOI
09 Aug 1990-Nature
TL;DR: The cloning and expression of a complementary DNA that encodes a G protein-coupled receptor that is involved in cannabinoid-induced CNS effects (including alterations in mood and cognition) experienced by users of marijuana are suggested.
Abstract: Marijuana and many of its constituent cannabinoids influence the central nervous system (CNS) in a complex and dose-dependent manner. Although CNS depression and analgesia are well documented effects of the cannabinoids, the mechanisms responsible for these and other cannabinoid-induced effects are not so far known. The hydrophobic nature of these substances has suggested that cannabinoids resemble anaesthetic agents in their action, that is, they nonspecifically disrupt cellular membranes. Recent evidence, however, has supported a mechanism involving a G protein-coupled receptor found in brain and neural cell lines, and which inhibits adenylate cyclase activity in a dose-dependent, stereoselective and pertussis toxin-sensitive manner. Also, the receptor is more responsive to psychoactive cannabinoids than to non-psychoactive cannabinoids. Here we report the cloning and expression of a complementary DNA that encodes a G protein-coupled receptor with all of these properties. Its messenger RNA is found in cell lines and regions of the brain that have cannabinoid receptors. These findings suggest that this protein is involved in cannabinoid-induced CNS effects (including alterations in mood and cognition) experienced by users of marijuana.

4,806 citations


Journal ArticleDOI
22 Nov 1990-Nature
TL;DR: It is demonstrated that Bcl-2 is an integral inner mitochondrial membrane protein of relative molecular mass 25,000 (25k) being localized to mitochondria and interfering with programmed cell death independent of promoting cell division.
Abstract: The t(14; 18) chromosomal translocation of human follicular B-cell lymphoma juxtaposes the bcl-2 gene with the immunoglobulin heavy chain locus. The bcl-2 immunoglobulin fusion gene is markedly deregulated resulting in inappropriately elevated levels of bcl-2 RNA and protein. Transgenic mice bearing a bcl-2 immunoglobulin minigene demonstrate a polyclonal expansion of resting yet responsive IgM-IgD B cells which display prolonged cell survival but no increase in cell cycling. Moreover, deregulated bcl-2 extends the survival of certain haematopoietic cell lines following growth-factor deprivation. By using immunolocalization studies we now demonstrate that Bcl-2 is an integral inner mitochondrial membrane protein of relative molecular mass 25,000 (25k). Overexpression of Bcl-2 blocks the apoptotic death of a pro-B-lymphocyte cell line. Thus, Bcl-2 is unique among proto-oncogenes, being localized to mitochondria and interfering with programmed cell death independent of promoting cell division.

3,773 citations


Journal ArticleDOI
01 Oct 1990-Nature
TL;DR: In this paper, the trace-element geochemical properties of the adakites (termed "adakites") of modern island and continental arcs are shown to be consistent with a derivation by partial melting of the subducted slab, and in particular that subducting lithosphere younger than 25 Myr seems to be required for slab melting to occur.
Abstract: MOST volcanic rocks in modern island and continental arcs are probably derived from melting of the mantle wedge, induced by hydrous fluids released during dehydration reactions in the subducted lithosphere1. Arc tholeiitic and calc-alkaline basaltic magmas are produced by partial melting of the mantle, and then evolve by crystal fractionation (with or without assimilation and magma mixing) to more silicic magmas2—basalt, andesite, dacite and rhyolite suites. Although most arc magmas are generated by these petrogenetic processes, rocks with the geochemical characteristics of melts derived directly from the subducted lithosphere are present in some modern arcs where relatively young and hot lithosphere is being subducted. These andesites, dacites and sodic rhyolites (dacites seem to be the most common products) or their intrusive equivalents (tonalites and trondhjemites) are usually not associated with parental basaltic magmas3. Here we show that the trace-element geochemistry of these magmas (termed 'adakites') is consistent with a derivation by partial melting of the subducted slab, and in particular that subducting lithosphere younger than 25 Myr seems to be required for slab melting to occur.

3,524 citations


Journal ArticleDOI
18 Oct 1990-Nature
TL;DR: A member of the steroid hormone receptor superfamily of ligand-activated transcription factors is cloned that is activated by a diverse class of rodent hepatocarcinogens that causes proliferation of peroxisomes.
Abstract: We have cloned a member of the steroid hormone receptor superfamily of ligand-activated transcription factors. The receptor homologue is activated by a diverse class of rodent hepatocarcinogens that causes proliferation of peroxisomes. Identification of a peroxisome proliferator-activated receptor should help elucidate the mechanism of the hypolipidaemic effect of these hepatocarcinogens and aid evaluation of their potential carcinogenic risk to man.

3,370 citations


Journal ArticleDOI
06 Dec 1990-Nature
TL;DR: It is shown that complete antibody V domains can be displayed on the surface of fd bacteriophage, that the phage bind specifically to antigen and that rare phage can be isolated after affinity chromatography.
Abstract: NEW ways of making antibodies have recently been demonstrated using gene technology. Immunoglobulm variable (V) genes are amplified from hybridomas or B cells using the polymerase chain reaction, and cloned into expression vectors. Soluble antibody fragments secreted from bacteria are then screened for binding activities (see ref. 1 for review). Screening of V genes would, however, be revolutionized if they could be expressed on the surface of bacteriophage. Phage carrying V genes that encode binding activities could then be selected directly with antigen. Here we show that complete antibody V domains can be displayed on the surface of fd bacteriophage, that the phage bind specifically to antigen and that rare phage (one in a million) can be isolated after affinity chromatography.

Journal ArticleDOI
19 Jul 1990-Nature
TL;DR: A search of a 35-kilobase region of the human Y chromosome necessary for male sex determination has resulted in the identification of a new gene, termed SRY (for sex-determining region Y) and proposed to be a candidate for the elusive testis-d determining gene, TDF.
Abstract: A search of a 35-kilobase region of the human Y chromosome necessary for male sex determination has resulted in the identification of a new gene. This gene is conserved and Y-specific among a wide range of mammals, and encodes a testis-specific transcript. It shares homology with the mating-type protein, Mc, from the fission yeast Schizosaccharomyces pombe and a conserved DNA-binding motif present in the nuclear high-mobility-group proteins HMG1 and HMG2. This gene has been termed SRY (for sex-determining region Y) and proposed to be a candidate for the elusive testis-determining gene, TDF.

Journal ArticleDOI
25 Oct 1990-Nature
TL;DR: It is demonstrated that NO synthase in the brain to be exclusively associated with discrete neuronal populations, and prominent neural localizations provided the first conclusive evidence for a strong association of NO with neurons.
Abstract: Nitric oxide (NO), apparently identical to endothelium-derived relaxing factor in blood vessels, is also formed by cytotoxic macrophages, in adrenal gland and in brain tissue, where it mediates the stimulation by glutamate of cyclic GMP formation in the cerebellum Stimulation of intestinal or anococcygeal nerves liberates NO, and the resultant muscle relaxation is blocked by arginine derivatives that inhibit NO synthesis It is, however, unclear whether in brain or intestine, NO released following nerve stimulation is formed in neurons, glia, fibroblasts, muscle or blood cells, all of which occur in proximity to neurons and so could account for effects of nerve stimulation on cGMP and muscle tone We have now localized NO synthase protein immunohistochemically in the rat using antisera to the purified enzyme We demonstrate NO synthase in the brain to be exclusively associated with discrete neuronal populations NO synthase is also concentrated in the neural innervation of the posterior pituitary, in autonomic nerve fibres in the retina, in cell bodies and nerve fibres in the myenteric plexus of the intestine, in adrenal medulla, and in vascular endothelial cells These prominent neural localizations provide the first conclusive evidence for a strong association of NO with neurons

Journal ArticleDOI
Paul Nurse1
05 Apr 1990-Nature
TL;DR: The onset of M-phase is regulated by a mechanism common to all eukaryotic cells and requires p34cdc2 dephosphorylation and association with cyclin.
Abstract: The onset of M-phase is regulated by a mechanism common to all eukaryotic cells. Entry into M-phase is determined by activation of the p34cdc2 protein kinase which requires p34cdc2 dephosphorylation and association with cyclin.

Journal ArticleDOI
D. M. Eigler1, E. K. Schweizer1
01 Apr 1990-Nature
TL;DR: In this paper, Binnig and Rohrer used the scanning tunnelling microscope (STM) to position individual xenon atoms on a single-crystal nickel surface with atomic pre-cision.
Abstract: SINCE its invention in the early 1980s by Binnig and Rohrer1,2, the scanning tunnelling microscope (STM) has provided images of surfaces and adsorbed atoms and molecules with unprecedented resolution The STM has also been used to modify surfaces, for example by locally pinning molecules to a surface3 and by transfer of an atom from the STM tip to the surface4 Here we report the use of the STM at low temperatures (4 K) to position individual xenon atoms on a single-crystal nickel surface with atomic pre-cision This capacity has allowed us to fabricate rudimentary structures of our own design, atom by atom The processes we describe are in principle applicable to molecules also In view of the device-like characteristics reported for single atoms on surfaces5,6, the possibilities for perhaps the ultimate in device miniaturization are evident

Journal ArticleDOI
13 Sep 1990-Nature
TL;DR: The D3 receptor is localized to limbic areas of the brain, which are associated with cognitive, emotional and endocrine functions, and seems to mediate some of the effects of antipsychotic drugs and drugs used against Parkinson's disease.
Abstract: A dopamine receptor has been characterized which differs in its pharmacology and signalling system from the D1 or D2 receptor and represents both an autoreceptor and a postsynaptic receptor The D3 receptor is localized to limbic areas of the brain, which are associated with cognitive, emotional and endocrine functions It seems to mediate some of the effects of antipsychotic drugs and drugs used against Parkinson's disease, that were previously thought to interact only with D2 receptors

Journal ArticleDOI
01 Dec 1990-Nature
TL;DR: The cloning of a complementary DNA encoding a bovine endothelin receptor is reported, which has a transmembrane topology similar to that of other G protein-coupled receptors and shows specific binding, with the highest selectivity to ET-1 in animal cells trans-fected with the cloned cDNA.
Abstract: Endothelins are a newly described peptide family consisting of three peptides (ET-1, ET-2 and ET-3) which are the most potent vasoconstrictive peptides known. They are crucial in the regulation of vascular smooth muscle tone. The diverse functions of endothelins are thought to be mediated by interaction with many different receptors coupled to the inositol phosphate/calcium ion messenger pathway. However, because of the structural resemblance of the three peptides, the presence and nature of multiple endothelin receptors remain to be elucidated. We report here the cloning of a complementary DNA encoding a bovine endothelin receptor, which has a transmembrane topology similar to that of other G protein-coupled receptors and shows specific binding, with the highest selectivity to ET-1 in animal cells transfected with the cloned cDNA. This receptor messenger RNA is widely distributed in the central nervous system and peripheral tissues, particularly in the heart and lung. Our results support the view that there are other receptor subtypes.

Journal ArticleDOI
01 Dec 1990-Nature
TL;DR: The cloning of a complementary DNA encoding one subtype belonging to the superf amily of G protein-coupled receptors is reported, indicating that this cDNA encodes a 'nonselective' subtype of the receptor which is different from the vascular smooth muscle receptor.
Abstract: ENDOTHELIN-1 was initially identified as a 21-residue potent vasoconstrictor peptide produced by vascular endothelial cells, but was subsequently found to have many effects on both vascular and non-vascular tissues1,2. The discovery of three isopeptides of the endothelin family3, ET-1, ET-2 and ET-3, each possessing a diverse set of pharmacological activities of different potency, suggested the existence of several different endothelin receptor subtypes3–7. Endothelins may elicit biological responses by various signal-transduction mechanisms, including the G protein-coupled activation of phospholipase C and the activation of voltage-dependent Ca2+ channels8–10. Thus, different subtypes of the endothelin receptor may use different signal-transduction mechanisms. Here we report the cloning of a complementary DNA encoding one subtype belonging to the superf amily of G protein-coupled receptors. COS-7 cells transfected with the cDNA express specific and high-affinity binding sites for endothelins, responding to binding by the production of inositol phosphates and a transient increase in the concentration of intracellular free Ca2+. The three endothelin isopeptides are roughly equipotent in displacing 125I-labelled ET-1 binding and causing Ca2+ mobilization. A messenger RNA corresponding to the cDNA is detected in many rat tissues including the brain, kidney and lung but not in vascular smooth muscle cells. These results indicate that this cDNA encodes a 'nonselective' subtype of the receptor which is different from the vascular smooth muscle receptor.

Journal ArticleDOI
08 Nov 1990-Nature
TL;DR: A molecular switch is a molecular switch whose "on" and "off" states are triggered by binding and hydrolysis of GTP as discussed by the authors. But the mechanism in myriad versions of the switch can be traced back to a single primordial protein.
Abstract: Proteins that bind and hydrolyse GTP are being discovered at a rapidly increasing rate. Each of these many GTPases acts as a molecular switch whose 'on' and 'off' states are triggered by binding and hydrolysis of GTP. Conserved structure and mechanism in myriad versions of the switch--in bacteria, yeast, flies and vertebrates--suggest that all derive from a single primordial protein, repeatedly modified in the course of evolution to perform a dazzling variety of functions.

Journal ArticleDOI
13 Dec 1990-Nature
TL;DR: An A-to-G transition mutation at nucleotide pair 3,243 in the dihydrouridine loop of mitochondrial tRNALeu(UUR) that is specific to patients with MELAS is reported, which creates an Apal restriction site and could perform a simple molecular diagnostic test for the disease.
Abstract: MITOCHONDRIAL encephalomyopathies are usually divided into three distinct clinical subgroups: (1) mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS); (2) myoclonus epilepsy associated with ragged-red fibres (MERRF); and (3) chronic progressive external ophthalmoplegia (CPEO) including Kearns-Sayre syndrome1–5. Large deletions of human mitochondrial DNA and a transition mutation at the mitochondrial transfer RNAlys gene give rise to CPEO including Kearns–Sayre syndrome6–8 and MERRF9,10, respectively. Here we report an A-to-G transition mutation at nucleotide pair 3,243 in the dihydrouridine loop of mitochondrial tRNALeu(UUR) that is specific to patients with MELAS. Because this mutation creates an Apal restriction site, we could perform a simple molecular diagnostic test for the disease. The mutation was present in 26 out of 31 independent MELAS patients and 1 out of 29 CPEO patients, but absent in the 5 MERRF and 50 controls tested. Southern blot analysis confirmed that the mutant DNA always coexists with the wild-type DNA (heteroplasmy).

Journal ArticleDOI
31 May 1990-Nature
TL;DR: It is shown that op/op fibroblasts are defective in production of functional macrophage colony-stimulating factor (M-CSF), although its messenger RNA (Csfm mRNA) is present at normal levels, and it is concluded that the pathological changes in this mutant result from the absence of M- CSF.
Abstract: Mice homozygous for the recessive mutation osteopetrosis (op) on chromosome 3 have a restricted capacity for bone remodelling, and are severely deficient in mature macrophages and osteoclasts. Both cell populations originate from a common haemopoietic progenitor. As op/op mice are not cured by transplants of normal bone marrow cells, the defects in op/op mice may be associated with an abnormal haematopoietic microenvironment rather than with an intrinsic defect in haematopoietic progenitors. To investigate the molecular and biochemical basis of the defects caused by the op mutation, we established primary fibroblast cell lines from op/op mice and tested the ability of these cell lines to support the proliferation of macrophage progenitors. We show that op/op fibroblasts are defective in production of functional macrophage colony-stimulating factor (M-CSF), although its messenger RNA (Csfm mRNA) is present at normal levels. This defect in M-CSF production and the recent mapping of the Csfm structural gene near op on chromosome 3 suggest that op is a mutation within the Csfm gene itself. We have sequenced Csfm complementary DNA prepared from op/op fibroblasts and found a single base pair insertion in the coding region of the Csfm gene that generates a stop codon 21 base pairs downstream. Thus, the op mutation is within the Csfm coding region and we conclude that the pathological changes in this mutant result from the absence of M-CSF.

Journal ArticleDOI
06 Sep 1990-Nature
TL;DR: The atomic models of the complex between rabbit skeletal muscle actin and bovine pancreatic deoxyribonuclease I both in the ATP and ADP forms have been determined byo X-ray analysis at an effective resolution of 2.8 Å and 3 Å.
Abstract: The atomic models of the complex between rabbit skeletal muscle actin and bovine pancreatic deoxyribonuclease I both in the ATP and ADP forms have been determined by X-ray analysis at an effective resolution of 2.8 A and 3A, respectively. The two structures are very similar. The actin molecule consists of two domains which can be further subdivided into two subdomains. ADP or ATP is located in the cleft between the domains with a calcium ion bound to the beta- or beta- and gamma-phosphates, respectively. The motif of a five-stranded beta sheet consisting of a beta meander and a right handed beta alpha beta unit appears in each domain suggesting that gene duplication might have occurred. These sheets have the same topology as that found in hexokinase.

Journal ArticleDOI
30 Aug 1990-Nature
TL;DR: It is shown that in most of the colorectal carcinomas that were analysed, there is a reduction in the length of telomere repeat arrays relative to the normal colonic mucosa from the same patient, and it is proposed that the telomerase2–4 is inactive in somatic tissues, andTelomere length is an indicator of the number of cell divisions that it has taken to form a particular tissue and possibly to generate tumours.
Abstract: We have hypothesized that end-to-end chromosome fusions observed in some tumours could play a part in genetic instability associated with tumorigenesis and that fusion may result from the loss of the long stretches of G-rich repeats found at the ends of all linear chromosomes. We therefore asked whether there is telomere loss or reduction in common tumours. Here we show that in most of the colorectal carcinomas that we analysed, there is a reduction in the length of telomere repeat arrays relative to the normal colonic mucosa from the same patient. We speculate on the consequences of this loss for tumorigenesis. We also show that the telomere arrays are much smaller in colonic mucosa and blood than in fetal tissue and sperm, and that there is a reduction in average telomere length with age in blood and colon mucosa. We propose that the telomerase is inactive in somatic tissues, and that telomere length is an indicator of the number of cell divisions that it has taken to form a particular tissue and possibly to generate tumours.

Journal ArticleDOI
03 May 1990-Nature
TL;DR: Germ-line transmission of the inactivated IGF-II gene from male chimaeras yielded heterozygous progeny that were smaller than their ES cell-derived wild-type littermates (about 60% of normal body weight) and these growth-deficient animals were otherwise apparently normal and fertile.
Abstract: Growth factors are thought to function as pivotal autocrine-paracrine regulatory signals during embryonic development. Insulin-like growth factor II (IGF-II), a mitogenic polypeptide for a variety of cell lines, could have such a role, as indicated by the pattern of expression of its gene during rodent development. The IGF-II gene uses at least three promoters and expresses several transcripts in many tissues during the embryonic and neonatal periods, whereas expression in adult animals is confined to the choroid plexus and the leptomeninges. To examine the developmental role of IGF-II, we have begun to study the consequences of introducing mutations at the IGF-II gene locus in the mouse germ line. We have disrupted one of the IGF-II alleles in cultured mouse embryonic stem (ES) cells by gene targeting and constructed chimaeric animals. Germ-line transmission of the inactivated IGF-II gene from male chimaeras yielded heterozygous progeny that were smaller than their ES cell-derived wild-type littermates (about 60% of normal body weight). These growth-deficient animals were otherwise apparently normal and fertile. The effect of the mutation was exerted during the embryonic period. These results provide the first direct evidence for a physiological role of IGF-II in embryonic growth.

Journal ArticleDOI
19 Apr 1990-Nature
TL;DR: An approach is presented for making short-term predictions about the trajectories of chaotic dynamical systems, applied to data on measles, chickenpox, and marine phytoplankton populations, to show how apparent noise associated with deterministic chaos can be distinguished from sampling error and other sources of externally induced environmental noise.
Abstract: An approach is presented for making short-term predictions about the trajectories of chaotic dynamical systems. The method is applied to data on measles, chickenpox, and marine phytoplankton populations, to show how apparent noise associated with deterministic chaos can be distinguished from sampling error and other sources of externally induced environmental noise.

Journal ArticleDOI
03 May 1990-Nature
TL;DR: The phylogenetically analysed clone libraries of eubacterial 16S ribosomal RNA genes amplified from natural populations of Sargasso Sea picoplankton indicate the presence of a novel microbial group, the SAR 11 cluster, which appears to be a significant component of this oligotrophic bacterioplankton community.
Abstract: BACTERIOPLANKTON are recognized as important agents of biogeochemical change in marine ecosystems, yet relatively little is known about the species that make up these communities. Uncertainties about the genetic structure and diversity of natural bacterioplankton populations stem from the traditional difficulties associated with microbial cultivation techniques. Discrepancies between direct counts and plate counts are typically several orders of magnitude, raising doubts as to whether cultivated marine bacteria are actually representative of dominant planktonic species1–3. We have phylogenetically analysed clone libraries of eubacterial 16S ribosomal RNA genes amplified from natural populations of Sargasso Sea picoplankton by the polymerase chain reaction4. The analysis indicates the presence of a novel microbial group, the SAR 11 cluster, which appears to be a significant component of this oligotrophic bacterioplankton community. A second cluster of lineages related to the oxygenic phototrophs—cyanobacteria, prochlorophytes and chloroplasts—was also observed. However, none of the genes matched the small subunit rRNA sequences of cultivated marine cyanobacteria from similar habitats. The diversity of 16S rRNA genes observed within the clusters suggests that these bacterioplankton may be consortia of independent lineages sharing surprisingly distant common ancestors.

Journal ArticleDOI
06 Sep 1990-Nature
TL;DR: A unique orientation of the monomer with respect to the actin helix has been found and the main interactions are along the two-start helix with a contribution from a loop extending across the filament axis provided by the molecule in the adjacent strand.
Abstract: The F-actin filament has been constructed from the atomic structure of the actin monomer to fit the observed X-ray fibre diagram from oriented gels of F-actin. A unique orientation of the monomer with respect to the actin helix has been found. The main interactions are along the two-start helix with a contribution from a loop extending across the filament axis provided by the molecule in the adjacent strand. There are also contacts along the left-handed genetic helix.

Journal ArticleDOI
19 Jul 1990-Nature
TL;DR: A gene mapping to the sex-determining region of the mouse Y chromosome is deleted in a line of XY female mice mutant for Tdy, and is expressed at a stage during male gonadal development consistent with its having a role in testis determination.
Abstract: A gene mapping to the sex-determining region of the mouse Y chromosome is deleted in a line of XY female mice mutant for Tdy, and is expressed at a stage during male gonadal development consistent with its having a role in testis determination. This gene is a member of a new family of at least five mouse genes, related by an amino-acid motif showing homology to other known or putative DNA-binding domains.

Journal ArticleDOI
17 May 1990-Nature
TL;DR: By indicating the existence of an additional pathway through which retinoic acid may exert its effects, these data lead to a re-evaluation of retinoid physiology.
Abstract: Molecular cloning and transcriptional activation studies have revealed a new protein similar to the steroid hormone receptors and which responds specifically to vitamin A metabolites. This protein is substantially different in primary structure and ligand specificity from the products of the previously described retinoic acid receptor gene family. By indicating the existence of an additional pathway through which retinoic acid may exert its effects, these data lead to a re-evaluation of retinoid physiology.

Journal ArticleDOI
13 Sep 1990-Nature
TL;DR: The pancreatic islet β-cell autoantigen of relative molecular mass 64,000 (64K), which is a major target of autoantibodies associated with the development of insulin-dependent diabetes mel-litus (IDDM), has been identified as glutamic acid decarboxylase, the biosynthesizing enzyme of the inhibitory neurotransmitter GABA.
Abstract: The pancreatic islet β-cell autoantigen of relative molecular mass 64,000 (64K), which is a major target of autoantibodies associated with the development of insulin-dependent diabetes mel-litus (IDDM) has been identified as glutamic acid decarboxylase, the biosynthesizing enzyme of the inhibitory neurotransmitter GABA (γ-aminobutyric acid). Pancreatic β cells and a subpopulation of central nervous system neurons express high levels of this enzyme. Autoantibodies against glutamic acid decarboxylase with a higher titre and increased epitope recognition compared with those usually associated with IDDM are found in stiff-man syndrome, a rare neurological disorder characterized by a high coincidence with IDDM.