bluuebunny/crossref_metadata_2025 huggingface dataset:
A New DNA Marker Tightly Linked to the Fragile X Locus (
FRAXA
)
Authors: Suthers G. K. , Callen D. F. , Hyland V. J. , Kozman H. M. , Baker E. , Eyre H. , Harper P. S. , Roberts S. H. , Hors-Cayla M. C. , Davies K. E. , Bell M. V. , Sutherland G. R.
Published: October 2006

The fragile X syndrome is the most common cause of familial mental retardation. Genetic counseling and gene isolation are hampered by a lack of DNA markers close to the disease locus. Two somatic cell hybrids that each contain a human X chromosome with a breakpoint close to the fragile X locus have been characterized. A new DNA marker (
DXS296
) lies between the chromosome breakpoints and is the closest marker to the fragile X locus yet reported. The Hunter syndrome gene, which causes iduronate sulfatase deficiency, is located at the X chromosome breakpoint that is distal to this new marker, thus localizing the Hunter gene distal to the fragile X locus.
Bovine Leukemia Virus-Related Antigens in Lymphocyte Cultures Infected with AIDS-Associated Viruses
Authors: Thiry L. , Sprecher-Goldberger S. , Jacquemin P. , Cogniaux J. , Burny A. , Bruck C. , Portetelle D. , Cran S. , Clumeck N.
Published: October 2006

An earlier finding that lymphocytes from African patients with the acquired immune deficiency syndrome (AIDS) react with rabbit antiserum to purified antigens of bovine leukemia virus (BLV) prompted a study of the possible cross-reactions between a BLV-infected ovine cell line and human lymphocytes inoculated with a strain of lymphadenopathy syndrome-associated virus (LAV). A solid-phase radioimmunoassay was used to detect antigenic markers of the retroviruses. Crude extracts from short-term cultures of lymphocytes infected with LAV bound rabbit antisera to the LAV glycoprotein gp13 (molecular weight 13,000) and the BLV proteins p24 and gp51, but did not bind antibodies to the p24 of human T-cell leukemia virus type I (HTLV-I). Antiserum to LAV gp13 reacted with an ovine cell line producing BLV but also weakly with virus-free ovine cells. Lymphocyte cultures from four African patients with AIDS expressed BLV-related antigens within 6 to 10 days of culture, at the moment when particle-bound reverse transcriptase was produced. BLV-related antigens were induced in lymphocyte cultures from healthy individuals by addition of filtered supernatant or irradiated cells of the original culture. The antisera to BLV used in this study may prove useful for the detection of AIDS-associated viruses in short-term cultures of lymphocytes from AIDS patients or their contacts.
An Instability in Neutron Stars at Birth
Authors: Burrows Adam , Fryxell Bruce A.
Published: October 2006

Calculations with a two-dimensional hydrodynamic simulation show that a generic Raleigh-Taylor-like instability occurs in the mantles of nascent neutron stars, that it is possibly violent, and that the standard spherically symmetric models of neutron star birth and supernova explosion may be inadequate. Whether this "convective" instability is pivotal to the supernova mechanism, pulsar magnetic fields, or a host of other important issues that attend stellar collapse remains to be seen, but its existence promises to modify all questions concerning this most energetic of astronomical phenomena.
Infrared Reflection-Absorption Spectroscopy and STM Studies of Model Silica-Supported Copper Catalysts
Authors: Xu Xueping , Vesecky Scott M. , Goodman D. Wayne
Published: October 2006

The structure of model silica-supported copper catalysts has been investigated with scanning tunneling microscopy (STM) and infrared reflection-absorption spectroscopy (IRAS). The IRAS studies of CO on the model silica-supported copper catalysts indicate that there are several types of copper clusters with surface structures similar to (111), (110), and other high-index planes of single-crystal copper. The STM studies show several types of copper clusters on silica and reveal images of metal clusters on an amorphous oxide support with atomic resolution.
Chaotic Stirring in a Tidal System
Authors: Ridderinkhof H. , Zimmerman J. T. F.
Published: October 2006

An analysis of a two-dimensional tidal model of the Wadden Sea reveals Lagrangian chaos in the trajectories of water parcels. The associated chaotic stirring results from the transverse intersection of the stable and unstable curves of hyperbolic fixed points in the Lagrangian residual displacement field (the tidal Poincaré map). This tidal dispersion mechanism produces rapid water exchange along the channel axis and could be representative of many shallow tidal seas.
Excitation and Decay of Correlated Atomic States
Authors: Rau A. R. P.
Published: October 2006

Doubly excited states of atoms and ions in which two electrons are excited from the ground configuration display strong radial and angular electron correlations. They are prototypical examples of quantum-mechanical systems with strong coupling. Two distinguishing characteristics of these states are: (i) their organization into successive families, with only weak coupling between families, and (ii) a hierarchical nature of this coupling, with states from one family decaying primarily to those in the next lower family. A view of the pair of electrons as a single entity, with the electron-electron repulsion between them divided into an adiabatic and a nonadiabatic piece, accounts for many of the dominant features. The stronger, adiabatic part determines the family structure and the weaker, nonadiabatic part the excitation and decay between successive families. Similar considerations extend to three-electron atomic states, which group into five different classes. They are suggestive of composite models for quarks in elementary particle physics, which exhibit analogous groupings into families with a hierarchical arrangement of masses and electroweak decays.
Vapor Pressures of Solid Hydrates of Nitric Acid: Implications for Polar Stratospheric Clouds
Authors: Worsnop Douglas R. , Zahniser Mark S. , Fox Lewis E. , Wofsy Steven C.
Published: October 2006

Thermodynamic data are presented for hydrates of nitric acid: HNO
3
⋅H
2
O, HNO
3
⋅2H
2
O, HNO
3
⋅3H
2
O, and a higher hydrate. Laboratory data indicate that nucleation and persistence of metastable HNO
3
⋅2H
2
O may be favored in polar stratospheric clouds over the slightly more stable HNO
3
⋅3H
2
O. Atmospheric observations indicate that some polar stratospheric clouds may be composed of HNO
3
⋅2H
2
O and HNO
3
⋅3H
2
O. Vapor transfer from HNO
3
⋅2H
2
O to HNO
3
⋅3H
2
O could be a key step in the sedimentation of HNO
3
, which plays an important role in the depletion of polar ozone.
Mechanisms in the Competitive Success of an Invading Sexual Gecko over an Asexual Native
Authors: Petren Kenneth , Bolger Douglas T. , Case Ted J.
Published: October 2006

The competitive displacement by a sexual gecko species of an asexual resident gecko has been documented over a wide geographic area. To test hypotheses concerning the detailed mechanism of this displacement, an experimental system was developed to follow populations of geckos in a duplicated, controlled environment that closely approximates the natural arena for the competitive interaction. Asymmetric competition occurred only in the presence of light, which attracts a dense concentration of insect food sources. The mechanism of competition was partly due to the behavioral dominance of the larger sexual species over the smaller asexual species in areas near the concentrated food. However, this behavior resulted from an avoidance response of subordinate asexuals rather than overt aggression by the sexual species.
Transient Turing Structures in a Gradient-Free Closed System
Authors: Lengyel István , Kádár Sándor , Epstein Irving R.
Published: October 2006

Transient, symmetry-breaking, spatial patterns were obtained in a closed, gradient-free, aqueous medium containing chlorine dioxide, iodine, malonic acid, and starch at 4° to 5°C. The conditions under which these Turing-type structures appear can be accurately predicted from a simple mathematical model of the system. The patterns, which consist of spots, stripes, or both spots and stripes, require about 25 minutes to form and remain stationary for 10 to 30 minutes.
Order-Disorder Transition in Polycrystalline C
60
Films
Authors: Akers Kelly , Fu Kejian , Zhang Peng , Moskovits Martin
Published: October 2006

High-resolution Raman spectroscopy of polycrystalline films of C
60
deposited under ultrahigh-vacuum conditions show that the spectrum below 244 ± 3 kelvin consists of a superposition of two components whose relative contributions are temperature-dependent. The spectrum of the more intense of the two components is similar to that obtained for air- or oxygen-exposed samples of C
60
at room temperature, whereas the spectrum above 244 ± 3 kelvin corresponds to one previously reported for oxygen-free samples of C
60
. The results may indicate an order-disorder phase transition involving the percolation of a cluster of C
60
molecules engaged in coherent Raman scattering.
Isomers of Small Carbon Cluster Anions: Linear Chains with up to 20 Atoms
Authors: von Helden Gert , Kemper Paul R. , Gotts Nigel G. , Bowers Michael T.
Published: October 2006

The structure of small carbon cluster anions, C

n

-
(4 ≤
n
≤ 20), was investigated with the use of ion chromatography. With this technique, both the existence and the relative amounts of possible structural isomers can be determined. More than 99% of the ions C
5
-
to C
9
-
were found to be linear under these experimental conditions. Starting with C
10
-
, a monocyclic isomer was observed, and linear and moncyclic structures coexisted from C
10
-
through at least C
20
-
. This result is in contrast to previous work on positive ions, which showed the existence of linear isomers from C
5
+
to C
10
+
, with linear and cyclic isomers coexisting only from C
7
+
to C
10
+
. Above C
10
+
, no linear clusters were observed.
Researchers Defy the Physical Limits to Computation
Authors: Flam Faye
Published: October 2006

Each year's new computing technology, it seems, leaves the last year's in the dust. But physicists are now beginning to tell computer scientists that it can't go on this way. Sooner or later, as computers get smaller, faster, and more complex, the laws of physics will throw up roadblocks to further progress. There's only one way out of this bind: radically new strategies. And some of those strategies are starting to emerge.
Potassium Channels in
Samanea saman
Protoplasts Controlled by Phytochrome and the Biological Clock
Authors: Kim Hak Yong , Coté Gary G. , Crain Richard C.
Published: October 2006

Leaflet movement in legumes depends on rhythmic, light-regulated ion fluxes in opposing regions of the leaf-moving organ. In flexor and extensor protoplasts from
Samanea saman
Merrill, opening and closing of K
+
channels were rhythmic in constant darkness. When channels were open in flexor protoplasts they were closed in extensor protoplasts, and vice versa. The rhythms were shifted by a delay in the onset of constant darkness, a response typical of endogenous circadian rhythms. During the light period, the channels in flexor protoplasts were sensitive to red light that was followed by premature darkness; phytochrome was implicated as the photoreceptor.
Pattern Formation by Interacting Chemical Fronts
Authors: Lee Kyoung J. , McCormick W. D. , Ouyang Qi , Swinney Harry L.
Published: October 2006

Experiments on a bistable chemical reaction in a continuously fed thin gel layer reveal a new type of spatiotemporal pattern, one in which fronts propagate at a constant speed until they reach a critical separation (typically 0.4 millimeter) and stop. The resulting asymptotic state is a highly irregular stationary pattern that contrasts with the regular patterns such as hexagons, squares, and stripes that have been observed in many nonequilibrium systems. The observed patterns are initiated by a finite amplitude perturbation rather than through spontaneous symmetry breaking.
Fast Trap Jaws and Giant Neurons in the Ant
Odontomachus
Authors: Gronenberg Wulfila , Tautz Jürgen , Hölldobler Bert
Published: October 2006

Ants of the ponerine genus
Odontomachus
use a trap jaw mechanism when hunting fast prey. When particular trigger hairs, located on the inner edge of the mandibles, are touched by prey, the jaws close extremely rapidly and trap the target. This trap jaw response lasts only 0.33 to 1 millisecond. Electrophysiological recordings demonstrated that the trigger hairs function as mechanoreceptors. Associated with each trigger hair are large sensory cells, the sensory axons of which measure 15 to 20 micrometers in diameter. These are among the largest sensory neurons, and their size implies that these axons conduct information very rapidly.
Activation of the Cellular Proto-Oncogene Product p21Ras by Addition of a Myristylation Signal
Authors: Buss Janice E. , Solski Patricia A. , Schaeffer James P. , MacDonald Marsha J. , Der Channing J.
Published: October 2006

The 21-kD proteins encoded by
ras
oncogenes (p21Ras) are modified covalently by a palmitate attached to a cysteine residue near the carboxyl terminus. Changing cysteine at position 186 to serine in oncogenic forms produces a nonpalmitylated protein that fails to associate with membranes and does not transform NIH 3T3 cells. Nonpalmitylated p21Ras derivatives were constructed that contained myristic acid at their amino termini to determine if a different form of lipid modification could restore either membrane association or transforming activity. An activated p21Ras, altered in this way, exhibited both efficient membrane association and full transforming activity. Surprisingly, myristylated forms of normal cellular Ras were also transforming. This demonstrates that Ras must bind to membranes in order to transmit a signal for transformation, but that either myristate or palmitate can perform this role. However, the normal function of cellular Ras is diverted to transformation by myristate and therefore must be regulated ordinarily by some unique property of palmitate that myristate does not mimic. Myristylation thus represents a novel mechanism by which Ras can become transforming.
Influence of the Major Histocompatibility Complex on Positive Thymic Selection of V
β
17a
+
T Cells
Authors: Blackman Marcia A. , Marrack Philippa , Kappler John
Published: October 2006

A monoclonal antibody was used to show directly positive thymic selection of the T cell repertoire in mouse strains expressing the 17a β-chain variable domain (V
β
17a) of the T cell receptor. In the absence of the potent tolerizing class II major histocompatability complex (MHC) molecule, I-E, peripheral expression of V
β
17a
+
T cell receptors varied with the MHC haplotype of the mouse strain. In the most extreme case, H-2q mice expressed high peripheral levels of CD4
+
V
β
17a
+
T cells (14 to 19 percent), whereas H-2
b
mice expressed low levels (3 to 4 percent). Analysis of (b × q)F
1
mice and chimeric mice showed that these differences were determined by positive thymic selection and implicated the thymic epithelium as the controlling cell type.
Rat Brain
N
-Methyl-D-Aspartate Receptors Expressed in
Xenopus
oocytes
Authors: Verdoorn Todd A. , Kleckner Nancy W. , Dingledine Raymond
Published: October 2006

N
-methyl-D-aspartate (NMDA) activates a class of excitatory amino acid receptor involved in a variety of plastic and pathological processes in the brain. Quantitative study of the NMDA receptor has been difficult in mammalian neurons, because it usually exists with other excitatory amino acid receptors of overlapping pharmacological specificities.
Xenopus
oocytes injected with messenger RNA isolated from primary cultures of rat brain have now been used to study NMDA receptors. The distinguishing properties of neuronal NMDA receptors have been reproduced in this amphibian cell, including voltage-dependent block by magnesium, block by the NMDA receptor antagonist D-2-amino-5-phosphonovaleric acid, and potentiation by glycine. This preparation should facilitate the quantitative study of the regulation of NMDA receptor activation and serve as a tool for purification of the encoding messenger RNA.
A Mutation in the Catalytic Subunit of cAMP-Dependent Protein Kinase That Disrupts Regulation
Authors: Levin L. R. , Kuret J. , Johnson K. E. , Powers S. , Cameron S. , Michaeli T. , Wigler M. , Zoller M. J.
Published: October 2006

A mutant catalytic subunit of adenosine 3′,5′-monophosphate (cAMP)-dependent protein kinase has been isolated from
Saccharomyces cerevisiae
that is no longer subject to regulation yet retains its catalytic activity. Biochemical analysis of the mutant subunit indicates a 100-fold decreased affinity for the regulatory subunit. The mutant catalytic subunit exhibits approximately a threefold increase in Michaelis constant for adenosine triphosphate and peptide cosubstrates, and is essentially unchanged in its catalytic rate. The nucleotide sequence of the mutant gene contains a single nucleotide change resulting in a threonine-to-alanine substitution at amino acid 241. This residue is conserved in other serine-threonine protein kinases. These results identify this threonine as an important contact between catalytic and regulatory subunits but only a minor contact in substrate recognition.
A Common PDGF rEceptor Is Activated by Homodimeric A and B Forms of PDGF
Authors: Escobedo Jaime A. , Navankasatussas Sutip , Cousens Lawrence S. , Coughlin Shaun R. , Bell Graeme I. , Williams Lewis T.
Published: October 2006

The human platelet-derived growth factor (PDGF) receptor complementary DNA was cloned and expressed by transfection of Chinese hamster ovary (CHO) fibroblasts. The ability of CHO cells expressing the human receptor complementary DNA (CHO-HR5) to interact with different recombinant forms of PDGF (AA and BB homodimers) was tested. Both forms of PDGF bind to the transfected receptor, stimulate the receptor tyrosine kinase activity, and elicit a mitogenic response in a manner that was indistinguishable from the responses of Balb/c 3T3 cells. The data indicate that the tyrosine kinase and mitogenic responses of the Balb/c 3T3 cells to AA and BB forms of PDGF can be attributed to a single type of receptor and show that the AA form, like the BB form, is a true mitogen.
Conferring Operator Specificity on Restriction Endonucleases
Authors: Koob Michael , Grimes Eric , Szybalski Waclaw
Published: October 2006

Mapping and manipulation of very large genomes, including the human genome, would be facilitated by the availability of a DNA cleavage method with very high site specificity. Therefore, a general method was devised that extends the effective recognition sequences well beyond the present 8-base pair limit by combining the specificity of the restriction endonuclease with that of another sequence-specific protein that binds tightly to DNA. It was shown that the tightly binding
lac
or λ repressor protects a restriction site within the operator from specific modification methylases, M⋅Hha I or M⋅Hph I, while all other similar sites are methylated and thus rendered uncleavable. A plasmid containing a symmetric
lac
operator was specifically cleaved by Hha I, only at the site within the operator, after M⋅Hha I methylation in the presence of the
lac
repressor, whereas the remaining 31 Hha I sites on this plasmid were methylated and thus not cleaved. Analogous results were obtained with the Hae II site within the
lac
operator, which was similarly protected by the
lac
repressor, and with the Hph I site within the phage λ
o
L
operator, which was protected by λ repressor from M⋅Hph I methylation.
Methionine and Leucine Enkephalin in Rat Neurohypophysis: Different Responses to Osmotic Stimuli and T
2
Toxin
Authors: Zamir Nadav , Zamir Deganit , Eiden Lee E. , Palkovits Miklos , Brownstein Michael J. , Eskay Robert L. , Weber Eckard , Faden Alan I. , Feuerstein Giora
Published: October 2006

Specific radioimmunoassays were used to measure the effects of hypertonic saline (salt loading), water deprivation, and trichothecene mycotoxin (T
2
toxin) on the content of methionine enkephalin (ME), leucine enkephalin (LE), α-neoendorphin, dynorphin A, dynorphin B, vasopressin, and oxytocin in the rat posterior pituitary. Concentrations of vasopressin and oxytocin decreased in response to both osmotic stimuli and treatment with T
2
toxin, but the decrease was greater with osmotic stimulations. Similarly, concentrations of LE and dynorphin-related peptides declined after salt loading and water deprivation; LE concentrations also decreased after treatment with T
2
toxin. The concentration of ME decreased after water deprivation, did not change after salt loading, and increased after T
2
toxin treatment. The differentiating effects of these stimuli on the content of immunoreactive LE and ME are consistent with the hypothesis that LE and ME may be localized in separate populations of nerve endings with different roles in the posterior pituitary.
Neurons Containing NADPH-Diaphorase Are Selectively Resistant to Quinolinate Toxicity
Authors: Koh Jae-Young , Peters Stephen , Choi Dennis W.
Published: October 2006

Exposure of cultures of cortical cells from mouse to either of the endogenous excitatory neurotoxins quinolinate or glutamate resulted in widespread neuronal destruction; but only in the cultures exposed to quinolinate, an
N
-methyl-D-aspartate agonist, was there a striking preservation of the subpopulation of neurons containing the enzyme nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d). Further investigation revealed that neurons containing NADPH-d were also resistant to the toxicity of
N
-methyl-D-aspartate itself but were selectively vulnerable to the toxicity of either kainate or quisqualate. Thus, neurons containing NADPH-d may have an unusual distribution of receptors for excitatory amino acids, with a relative lack of
N
-methyl-D-aspartate receptors and a relative preponderance of kainate or quisqualate receptors. Since selective sparing of neurons containing NADPH-d is a hallmark of Huntington's disease, the results support the hypothesis that the disease may be caused by excess exposure to quinolinate or some other endogenous
N
-methyl-D-aspartate agonist.
Metabolic Correction of Defects in the Lipid Anchoring of Thy-1 in Lymphoma Mutants
Authors: Gupta Dwijendra , Tartakoff Alan , Tisdale Ellen
Published: October 2006

Many plasma membrane proteins, including Thy-1, are anchored by a carboxyl terminal glycophospholipid. This unit is absent from the Thy-1 of several lymphoma mutants that synthesize the Thy-1 polypeptide but fail to express it at the cell surface. Recessive mutants of complementation groups A to C, E, and F contain Thy-1 mRNA of normal size, which suggests that their Thy-1 polypeptide is normal. To identify possible metabolic lesions, each mutant was grown with various supplements. The class F and B mutants exhibited a reversible induction of surface lipid anchored Thy-1 when grown with the aminoglycoside G418. Other aminoglycosides, sugars, and ethanolamine were inactive. These unexpected observations are discussed in the context of lipid anchor biosynthesis.
Plasticity and Differentiation of Embryonic Retinal Cells After Terminal Mitosis
Authors: Adler Ruben , Hatlee Michael
Published: October 2006

The relation between terminal mitosis and the events that determine the developmental fate of embryonic precursor cells is not well understood. This relation has now been investigated with [
3
H]thymidine autoradiography to determine the time of cell birth and with a culture system that allows the testing of the developmental potential of cells isolated from the chick embryo retina. Contrary to the situation in vivo, where neuronal differentiation always precedes photoreceptor differentiation, photoreceptor differentiation occurs prematurely and precedes neuronal differentiation when precursor cells are isolated from the retina at early embryonic stages. Thus, cells born by embryonic day 5 (ED-5) give rise predominantly to photoreceptors when isolated for culture on ED-6 but develop mainly as neurons when isolated on ED-8. This suggests that retinal precursor cells retain after terminal mitosis the capacity to develop either as neurons or as photoreceptors. Moreover, photoreceptor differentiation appears to represent a constitutive or "default" pathway that precursor cells follow in the absence of neuron-inducing signals.
Circulating Atrial Natriuretic Peptides in Conscious Rats: Regulation of Release by Multiple Factors
Authors: Eskay Robert , Zukowska-Grojec Zofia , Haass Markus , Dave Jitendra R. , Zamir Nadav
Published: October 2006

Cardiocytes in the atria contain a prohormone that gives rise to atrial natriuretic peptides (ANP's), which have intrinsic hemodynamic regulatory activity. The distribution of ANP's in the brain suggests the involvement of these peptides in central cardiovascular regulation. In conscious rats with chronic indwelling catheters, volume loading with isotonic saline or glucose increased the amount of circulating immunoreactive ANP's by a factor of 4 to 5, as determined by radioimmunoassay. Hyperosmotic challenge with a hypertonic NaCl solution or anesthesia with halothane caused similar increases in plasma ANP's. Results obtained with the denervated-heart preparation indicate that neuronal influences are important in the release of ANP's induced by volume loading. As judged from reversed-phase high-performance liquid chromatography of extracted plasma and radioimmunoassay of collected fractions, the circulating physiologically important ANP's in the conscious rodent appear to be α-rANP(5-28) (atriopeptin III) and either α-rANP(3-28) [ANF(8-33)] or α-rANP(1-28) (ANF).
Multiple DNA-pRotein Interactions Governing High-Precision DNA Transactions
Authors: Echols Harrison
Published: October 2006

The precise association of DNA-binding proteins with localized regions of DNA is crucial for regulated replication and expression of the genome. For certain DNA transactions, the requirement for precision in localization and control is extremely high. High-precision events amenable to detailed biochemical analysis are the initiation of DNA replication and site-specific recombination by bacteriophage λ and
Escherichia coli
. Recent experiments indicate that site-localization and control in these reactions involves the association of DNA-bound proteins to generate organized nucleoprotein structures in which the DNA is folded or wound. These specialized nucleoprotein structures are likely to provide the requisite accuracy for site localization and the necessary regulated reactivity to direct the DNA transaction. Multiple DNA-protein interactions are also required for controlled transcription of the eukaryotic genome. Distant upstream regulator and enhancer sequences may define protein-binding sites that form part of a reactive nucleoprotein structure capable of initiating transcription.
Evidence for Reduced Recombination on the Nondisjoined Chromosomes 21 in Down Syndrome
Authors: Warren Andrew C. , Chakravarti Aravinda , Wong Corinne , Slaugenhaupt Susan A. , Halloran Susan L. , Watkins Paul C. , Metaxotou Caterina , Antonarakis Stylianos E.
Published: October 2006

Trisomy 21 usually results from nondisjunction during meiosis I. In order to determine whether nondisjunction results from failure of normal chromosome pairing or premature unpairing, recombination frequencies were estimated between DNA polymorphic markers on the long arm of chromosome 21 in families containing one individual with trisomy 21. The recombination frequencies on chromosomes 21 that had undergone nondisjunction were then compared to those on chromosomes 21 that had disjoined normally. The data indicate that recombination is reduced between DNA markers on nondisjoined chromosomes 21. These results are consistent with the hypothesis that reduced chiasma formation predisposes to nondisjunction, resulting in trisomy 21 in humans.
Activation of Adenovirus Promoters by the Adenovirus E1A Protein in Cell-Free Extracts
Authors: Spangler Rudolph , Bruner Mark , Dalie Barbara , Harter Marian L.
Published: October 2006

The primary product of the adenovirus E1A gene is a protein that is sufficient for controlling host-cell proliferation and immortalizing primary rodent cells. The mechanism by which the protein induces these cellular effects is poorly understood, but might be linked to its ability to regulate RNA transcription from a number of viral and cellular genes. The mechanism of E1A's transcriptional-activation (trans-activation) was studied here by monitoring the protein's effect on specific adenovirus promoters in two types of transcriptional systems in vitro. One of these systems consisted of extracts from transformed cells constitutively expressing E1A, and the other consisted of extracts of HeLa cells supplemented with a plasmid-encoded E1A protein purified from
Escherichia coli
. The results show that the E1A protein specifically stimulates transcription from adenovirus promoters; thus, the induction of cellular transcription factors is not necessary to explain the stimulation of transcription by E1A.
Enzyme Regulation in a Trypanosomatid: Effect of Purine Starvation on Levels of 3′-Nucleotidase Activity
Authors: Gottlieb Michael
Published: October 2006

Crithidia fasciculata
, a nonpathogenic relative of the leishmanial and trypanosomal pathogens of humans and animals, showed a 3′-ribonucleotidase activity similar to that in
Leishmania donovani
. The level of 3′-nucleotidase activity in
Crithidia
was regulated by the availability of purines in the culture medium. Specifically, organisms obtained from culture medium depleted of purines contained elevated levels of enzyme activity compared to those grown in complete medium. The 3′-nucleotidase, located at the cell surface, may serve as a first step in purine salvage for these protozoa, which are unable to synthesize the purine ring de novo.
Individual Tumors of Multifocal EB Virus-Induced Malignant Lymphomas in Tamarins Arise from Different B-Cell Clones
Authors: Cleary M. L. , Epstein M. A. , Finerty S. , Dorfman R. F. , Bornkamm G. W. , Kirkwood J. K. , Morgan A. J. , Sklar J.
Published: October 2006

Cotton-top tamarins were inoculated with sufficient Epstein-Barr virus to induce multiple tumors in each animal within 14 to 21 days. The tumors consisted of large-cell lymphomas that contained multiple copies of the Epstein-Barr virus genome and generated Epstein-Barr virus-carrying cell lines showing no detectable consistent chromosomal abnormality. Hybridization of tumor DNA with immunoglobulin gene probes revealed that each lymphoma was oligo- or monoclonal in origin and that individual tumors from the same animal arose from different B-cell clones. Thus the virus induced multiple transformation events in tamarins in vivo to cause malignant tumors resembling the Epstein-Barr virus-associated lymphomas of patients with organ transplants.
HTLV
x
-Gene Product: Requirement for the
env
Methionine Initiation Codon
Authors: Wachsman William , Golde David W. , Temple Patricia A. , Orr Elizabeth C. , Clark Steven C. , Chen Irvin S. Y.
Published: October 2006

The human T-cell leukemia viruses (HTLV) are replication-competent retroviruses whose genomes contain
gag
,
pol
, and
env
genes as well as a fourth gene, termed x, which is believed to be the transforming gene of HTLV. The product of the x gene is now shown to be encoded by a 2.1-kilobase messenger RNA derived by splicing of at least two introns. By means of S1 nuclease mapping of this RNA and nucleic acid sequence analysis of a complementary DNA clone, the complete primary structure of the x-gene product has been determined. It is encoded by sequences containing the
env
initiation codon and one nucleotide of the next codon spliced to the major open reading frame of the HTLV-I and HTLV-II x gene.
Cis
- and
Trans
-Acting Transcriptional Regulation of Visna Virus
Authors: Hess Jay L. , Clements Janice E. , Narayan Opendra
Published: October 2006

Visna virus is a pathogenic lentivirus of sheep that is related to human T-cell lymphotropic virus type III (HTLV-III), the probable etiologic agent of the acquired immune deficiency syndrome (AIDS). The transcriptional activity of visna virus promoter and enhancer sequences was studied by means of an assay based on the transient expression of the bacterial gene chloramphenicol acetyltransferase (CAT). The results suggest that the high level of expression of visna virus is due in part to
cis
-acting enhancer sequences that give the viral promoter a high level of transcriptional activity. In addition, the rate of transcription from the visna virus promoter situated in a plasmid expressing the CAT gene was much greater in infected than uninfected cells. This phenomenon of trans-acting transcriptional activation may involve either virally or cellularly encoded factors.
Genetic Engineering of Novel Genomes of Large DNA Viruses
Authors: Roizman Bernard , Jenkins Frank J.
Published: October 2006

Analyses of the function of specific genes and sequences of large DNA viruses such as herpesviruses and poxviruses present special problems because of the size of their genomes (120 to 250 kilobase pairs). Various methods for engineering site-specific insertions or deletions based on the use of selectable markers have been developed and applied for the elucidation of the function of specific DNA sequences, the identification of genes nonessential for virus growth in cell culture, and the expression of foreign genes. These methods should also make possible the construction of viral vectors capable of delivering genes specifying antigens for the prevention of infectious diseases in humans and animals.
Evidence That the v-
sis
Gene Product Transforms by Interaction with the Receptor for Platelet-Derived Growth Factor
Authors: Leal Fernando , Williams Lewis T. , Robbins Keith C. , Aaronson Stuart A.
Published: October 2006

A scheme for partial purification of biologically active v-
sis
-coded protein from cells transformed with simian sarcoma virus (SSV) has made possible a functional comparison of the transforming protein with platelet-derived growth factor (PDGF). The SSV-transforming gene product is capable of specifically binding PDGF receptors, stimulating tyrosine phosphorylation of PDGF receptors, and inducing DNA synthesis in quiescent fibroblasts. Each of these activities was specifically inhibited by antibodies to different regions of the v-
sis
gene product. Moreover, viral infection of a variety of cell types revealed a strict correlation between those cells possessing PDGF receptors and those susceptible to transformation by SSV. These findings provide evidence that SSV-transforming activity is mediated by the interaction of a virus-coded mitogen with PDGF receptors.
AIDS Retrovirus (ARV-2) Clone Replicates in Transfected Human and Animal Fibroblasts
Authors: Levy Jay A. , Cheng-Mayer Cecilia , Dina Dino , Luciw Paul A.
Published: October 2006

A molecular clone of the AIDS-associated retrovirus (ARV-2) was transfected into human T lymphocyte and monocyte cell lines as well as mouse, mink, monkey, and human fibroblast lines. A replicating virus with cytopathic and biologic properties of ARV-2 was recovered from all the cell lines. The animal and human fibroblast cells are resistant to direct infection by ARV, and in these experiments virus production in the fibroblast lines, especially mouse, was reduced compared to human lymphocytes. However, human fibroblasts were more permissive to virus expression than mouse cells. These results show that, whereas the primary block to ARV infection in certain cells may occur at the cell surface, intracellular mechanisms can also participate in controlling virus replication. The results have relevance to vaccine development and encourage further work with modified molecular clones to examine regions of the ARV genome necessary for cytopathology and replication.
Molecular Analysis of the Hotspot of Recombination in the Murine Major Histocompatibility Complex
Authors: Kobori Joan A. , Strauss Erich , Minard Karyl , Hood Leroy
Published: October 2006

Biological and serological assays have been used to define four subregions for the I region of the major histocompatibility complex (MHC) in the order I-A, I-B, I-J, and I-E. The I-J subregion presumably encodes the I-J polypeptide of the elusive T-cell suppressor factors. Restriction enzyme site polymorphisms and DNA sequence analyses of the I region from four recombinant mouse strains were used to localize the putative I-B and I-J subregions to a 1.0-kilobase (kb) region within the E
β
gene. Sequencing this region from E
β
clones derived from the two mouse strains: B10.A(3R), I-J
b
and B10.A(5R), I-J
k
initially used to define the I-J subregion revealed that these regions are identical, hence the distinct I-J
b
and I-J
k
molecules cannot be encoded by this DNA. In addition, the DNA sequence data also refute the earlier mapping of the I-B subregion. Analysis of the DNA sequences of three parental and four I region recombinants reveals that the recombinant events in three of the recombinant strains occurred within a 1-kb region of DNA, supporting the proposition that a hotspot for recombination exists in the I region. The only striking feature of this hotspot is a tetramer repeat (AGGC)

n

that shows 80 percent homology to the minisatellite sequence which may facilitate recombination in human chromosomes.
Simultaneous Effects of Erythropoietin and Colony-Stimulating Factor on Bone Marrow Cells
Authors: Van Zant Gary , Goldwasser Eugene
Published: October 2006

Erythropoietin or colony-stimulating factor, or both, were added to rat or mouse marrow cell cultures, and the responses to each inducer were measured. Colony-stimulating factor caused the suppression of erythropoietin-stimulated hemoglobin synthesis, and erythropoietin caused the suppression of the granulocyte-macrophage colony formation that is dependent on colony-stimulating factor. The extent of suppression by each inducer was dose-dependent. Marrow cells from plethoric rats were more sensitive to suppression of erythropoietin action by colony-stimulating factor than were normal marrow cells. These findings suggest that either (i) the receptors for erythropoietin and for colony-stimulating factor have overlapping specificities and that the "wrong" inducer may bind without having an inductive effect, or (ii) the target cells for erythropoietin and colony-stimulating factor are very closely related or are the same.
Megabase-Scale Mapping of the HLA Gene Complex by Pulsed Field Gel Electrophoresis
Authors: Lawrance Simon K. , Smith Cassandra L. , Srivastava Rakesh , Cantor Charles R. , Weissman Sherman M.
Published: October 2006

In the study of the genetic structure of mammalian chromosomes, there exists a "resolution gap" between molecular cloning experiments and meiotic linkage analyses. This gap has discouraged attempts to construct full-scale genetic maps of mammalian chromosomes. The organization of the human major histocompatibility complex was examined within this range by pulsed field gel electrophoresis. The data obtained indicate that the complex spans over 3000 kilobases and enable the construction of a megabase-scale molecular map. These results indicate that the techniques employed in DNA extraction, enzymatic digestion, electrophoresis, and hybridization are suitable for the efficient analysis of megabase regions of mammalian chromosomes and effectively bridge the resolution gap between molecular cloning and classical genetics.
Transposition of Gram-Positive Transposon Tn
916
in
Acholeplasma laidlawii
and
Mycoplasma pulmonis
Authors: Dybvig Kevin , Cassell Gail H.
Published: October 2006

Mycoplasma genetics has been limited by a lack of genetic tools such as selectable markers, methods to transfer DNA, and suitable vectors for cloning. Studies were undertaken to examine the potential of using the streptococcal transposon Tn
916
as a mycoplasma genetic tool. The
Escherichia coli
plasmid pAM120, which contains Tn
916
, was transformed into
Acholeplasma laidlawii
and
Mycoplasma pulmonis
. Transposition of Tn
916
into the mycoplasma chromosome apparently occurred by an excision-insertion mechanism. This example shows that newly introduced DNA from other bacteria can be successfully expressed in mycoplasma and that Tn
916
should serve as a powerful genetic tool for the study of mycoplasmas.
Efficient Packaging of Readthrough RNA in ALV: Implications for Oncogene Transduction
Authors: Herman Steven A. , Coffin John M.
Published: October 2006

Readthrough viral transcripts are present at relatively high levels in cells infected with avian leukosis virus. It has been proposed that they can function as intermediates in the transduction of proto-oncogenes by retroviruses. It is shown here, by the analysis of viruses containing a mutation in the AAUAAA polyadenylation signal, that readthrough RNAs have the requisite properties to function as transduction intermediates: (i) readthrough RNAs were polyadenylated and packaged as efficiently as normal viral RNA, (ii) RNAs nearly 11.2 kilobases (3.5 kilobases larger than wild-type avian leukosis virus genomes) were present in virions of the mutant virus, and (iii) virus particles containing both readthrough and normal genomes were most likely infectious.
Activation of Muscarinic Potassium Currents by ATPγS in Atrial Cells
Authors: Otero Angela S. , Breitwieser Gerda E. , Szabo Gabor
Published: October 2006

Intracellular perfusion of atrial myocytes with adenosine 5′-(γ-thio) triphosphate (ATPγS), an ATP analog, elicits a progressive increase of the muscarinic potassium channel current,
I
K(M)
, in the absence of agonists. In this respect, ATPγS mimics the actions of guanosine triphosphate (GTP) analogs, which produce direct, persistent activation of the guanyl nucleotide-binding (G) protein controlling the K
+
(M)
channel. The effect of ATPγS on
I
K(M)
, however, differs from that produced by GTP analogs in two aspects: it requires relatively large ATPγS concentrations, and it appears after a considerable delay, suggesting a rate-limiting step not present in similar experiments performed with guanosine 5′-(γ-thio) triphosphate (GTPγS). Incubation of atrial homogenates with [
35
S]ATPγS leads to formation of significant amounts of [
35
S]GTPγS, suggesting that activation of
I
K(M)
by ATPγS arises indirectly through its conversion into GTPγS by cellular enzymes. ATPγS is often used to demonstrate the involvement of protein phosphorylation in the control of various cellular processes. The finding that cytosolic application of ATPγS can also lead to G-protein activation implies that experiments with ATPγS must be interpreted with caution.
Isolated Retinas Synthesize Visual Pigments from Retinol Congeners Delivered by Liposomes
Authors: Uoshikami S. , Nöll G. N.
Published: October 2006

Isolated vertebrate retinas bathed in circulating Ringer solution cannot regenerate all of their bleached visual pigments. When dioleoyl-lecithin vesicles containing certain retinol congeners are added to the Ringer solution, such retinas begin to regenerate pigment immediately. The visual pigment of a bleached perfused retina can now be restored fully, making the isolated retina an independent unit for study. Liposomes can protect oxygen-sensitive, lipid-soluble substances and deliver them to living cells.
Protein Modification by Amino Acid Addition Is Increased in Crushed Sciatic But Not Optic Nerves
Authors: Shyne-Athwal S. , Riccio R. V. , Chakraborty G. , Ingoglia N. A.
Published: October 2006

Rat optic and sciatic nerves were crushed, and 10 minutes to 3 days later nerve segments between the crushed site and the cell body were removed and assayed for posttranslational protein modification by amino acid addition. Protein modification was comparable in intact optic and sciatic nerves, but in sciatic nerves increased to 1.6 times control levels 10 minutes after crushing and reached a maximum of ten times control levels by 2 hours. In optic nerves activity was decreased throughout the time course studied. The results indicate that, in a nerve which is capable of regeneration (sciatic), protein modification by the addition of amino acids increases immediately after injury, but a nerve incapable of regeneration (optic) is incapable of activating the modification reaction. These findings may be important in understanding the reasons for the lack of a regenerative response after injury to central mammalian nerves.
Mammalian Metallothionein Is Functional in Yeast
Authors: Thiele Dennis J. , Walling Mary Jane , Hamer Dean H.
Published: October 2006

Expression of two monkey metallothioneins in yeast leads to complementation of both known functions of the endogenous yeast copperthionein gene, namely copper detoxification and autoregulation of transcription. The metallothionein-like proteins of higher and lower eukaryotes are therefore functionally analogous despite their dissimilar primary sequences.
Tissue-Specific Expression of Functionally Rearranged λ1 Ig Gene Through a Retrovirus Vector
Authors: Cone Roger D. , Reilly Edward B. , Eisen Herman N. , Mulligan Richard C.
Published: October 2006

To explore the potential use of retrovirus vectors for the transfer of genomic DNA sequences into mammalian cells, recombinant retroviral genomes were constructed that encode a functionally rearranged murine λ 1 immunoglobulin gene. Several of these genomes could be transmitted intact to recipient cells by viral infection, although successful transmission depended both on the orientation of the λ 1 sequences and on their specific placement within vector sequences. The λ 1 gene transduced by viral infection was expressed in a cell lineage-specific manner, albeit at lower levels than endogenous λ 1 gene expression in cells from the B-lymphocyte lineage. Vectors yielding integrated proviruses that lacked viral transcriptional enhancer sequences were used to show that neither viral transcription nor the viral transcriptional sequences themselves had any effect on the tissue specificity of λ 1 gene expression or the absolute amount of λ 1 transcription. Vector transcription did, however, dramatically decrease the amount of λ 1 protein that could be detected in transduced cells. These results suggest that retrovirus vectors may be useful reagents not only for the expression of complementary DNA sequences but also for studies of tissue-specific transcription in mammalian cells.
Cloning of Yeast Transfer RNA Genes in
Escherichia coli
Authors: Beckmann Jacques S. , Johnson Peter F. , Abelson John
Published: October 2006

Four thousand
Escherichia coli
clones containing yeast DNA inserted into the plasmid pBR313 have been isolated. Of these, 175 clones were identified as carrying yeast transfer RNA genes. The initial analysis of the inserted transfer RNA genes via the colony hybridization technique with individual radioactive transfer RNA species is reported. The data indicate that yeast transfer RNA genes are not highly clustered, although some clustering exists. In addition, it was observed that the reiteration number of different transfer RNA genes may vary extensively.
The Effects of
Escherichia coli
and Yeast DNA Insertions on the Growth of Lambda Bacteriophage
Authors: Cameron John R. , Davis Ronald W.
Published: October 2006

The effects of Eco RI endonuclease-cleaved
Escherichia coli
and yeast (
Saccharomyces cerevisiae
) DNA fragments on the propagation of the lambda bacteriophage vectors containing them were determined on a nonmutated and a PolA
E. coli
K12 host. Observable alterations in the growth of hybrids containing yeast DNA insertions were less frequent and less extreme than those seen in hybrids containing
E. coli
DNA. A lambda-
E. coli
hybrid was selected after extensive growth on the PolA (deficient in polymerase I) host which also grew very well on the PolA
+
host and may have resulted from some alteration in the hybrid. Hybrids selected on the PolA host gave no evidence for the expression of polymerase I activity. No lambda-yeast hybrid made from the λgt vector lacking lambda-specific recombination (red
-
) had a yield of viable bacteriophage on infection greater than two-thirds that of "wild-type" lambda.