bluuebunny/crossref_metadata_2025 huggingface dataset:
Fabrication and Magnetic Properties of Arrays of Metallic Nanowires
Authors: Whitney T. M. , Searson P. C. , Jiang J. S. , Chien C. L.
Published: October 2006

Arrays of ferromagnetic nickel and cobalt nanowires have been fabricated by electrochemical deposition of the metals into templates with nanometer-sized pores prepared by nuclear track etching. These systems display distinctive characteristics because of their one-dimensional microstructure. The preferred magnetization direction is perpendicular to the film plane. Enhanced coercivities as high as 680 oersteds and remnant magnetization up to 90 percent have also been observed.
Orphan Strontium-87 in Abyssal Peridotites: Daddy Was a Granite
Authors: Snow Jonathan E. , Hart Stanley R. , Dick Henry J. B.
Published: October 2006

The
87
Sr/
86
Sr ratios in some bulk abyssal and alpine peridotites are too high to be binary mixtures of depleted mantle and seawater components. The apparent excess, or "orphan,"
87
Sr appears to be separated from its radioactive parent. Such observations were widely held to be analytical artifacts. Study of several occurrences of orphan
87
Sr shows that the orphan component in abyssal peridotite is located in the alteration products of olivine and enstatite in the peridotite. The orphan
87
Sr is most likely introduced by infiltration of low-temperature (<200°C) seawater bearing suspended detrital particulates. These particulates include grains of detrital clay that are partly derived from continental (that is, granitic) sources and thus are highly radiogenic. Orphan
87
Sr and other radiogenic isotopes may provide a tracer for low-temperature seawater penetrating into the oceanic crust.
Molecular Light Emission Induced by Inelastic Electron Tunneling
Authors: Flaxer Eli , Sneh Ofer , Cheshnovsky Ori
Published: October 2006

Light emission from molecular layers has been induced by inelastically tunneling electrons in a tunneling junction. The fast quenching of molecular emission on metal surfaces was suppressed by use of the "transparent conductor" indium-tin-oxide for the junction electrodes. The emission measurements have been made in squeezable tunneling junctions as small as 10
–9
square centimeters, coated with 9-10 dichloro-anthracene layers. At a bias of 2.5 to 3.5 volts, yields of 5000 photons per microcoulomb were observed. Evidence for the molecular origin of the emission is given. This method shows good prospects for use in the imaging of chromophores on surfaces with atomic resolution.
Correct Folding of Circularly Permuted Variants of a βα Barrel Enzyme in Vivo
Authors: Luger Karolin , Hommel Ulrich , Herold Marzell , Hofsteenge Jan , Kirschner Kasper
Published: October 2006

An important question in protein folding is whether the natural amino and carboxyl termini and the given order of secondary structure segments are critical to the stability and to the folding pathway of proteins. Here it is shown that two circularly permuted versions of the gene of a single-domain βα barrel enzyme can be expressed in
Escherichia coli
. The variants are enzymically active and are practically indistinguishable from the original enzyme by several structural and spectroscopic criteria, despite the creation of new termini and the cleavage of a surface loop. This novel genetic approach should be useful for protein folding studies both in vitro and in vivo.
Nucleotides in Yeast tRNA
Phe
Required for the Specific Recognition by Its Cognate Synthetase
Authors: Sampson Jeffrey R. , DiRenzo Anthony B. , Behlen Linda S. , Uhlenbeck Olke C.
Published: October 2006

An analysis of the aminoacylation kinetics of unmodified yeast tRNA
Phe
mutants revealed that five single-stranded nucleotides are important for its recognition by yeast phenylalanyl-tRNA synthetase, provided they were positioned correctly in a properly folded tRNA structure. When four other tRNAs were changed to have these five nucleotides, they became near-normal substrates for the enzyme.
Triggering of Allostery in an Enzyme by a Point Mutation: Ornithine Transcarbamoylase
Authors: Kuo Lawrence C. , Zambidis Ilias , Caron Connie
Published: October 2006

The origin of allostery is an unanswered question in the evolution of complex regulatory proteins. Anabolic ornithine transcarbamoylase, a trimer of identical subunits, is not an allosteric enzyme per se. However, when the active-site residue arginine-106 of the
Escherichia coli
enzyme is replaced with a glycine through site-directed mutagenesis, the resultant mutant enzyme manifests substrate cooperativity that is absent in the wild-type enzyme. Both homotropic and heterotropic interactions occur in the mutant enzyme. The initial velocity saturation curves of the substrates, carbamoyl phosphate and L-ornithine, conform to the Hill equation. The observed cooperativity depends on substrate but not enzyme concentration. The finding underscores the possibility that a single mutation of the enzyme in the cell could turn transcarbamoylation into a regulatory junction in the biosynthesis of L-arginine and urea.
Inducibility of Transferrin Receptors on Friend Erythroleukemic Cells
Authors: Hu Hsiang-Yun Yang , Gardner Joseph , Aisen Philip , Skoultchi Arthur I.
Published: October 2006

The ability of Friend erythroleukemic cells to bind transferrin and take up its iron increases substantially as a result of dimethyl sulfoxide-stimulated differentiation. Although transferrin-binding activity is also demonstrable in another mouse cell line of hematopoietic origin, the lymphoma cell, it does not increase on exposure to dimethyl sulfoxide. Gel filtration studies corroborate that the binding of transferrin to the erythroleukemic cells is due to the formation of a specific complex of transferrin and a membrane receptor. Thus, the specific interaction of transferrin with its receptor is another expression of dimethyl sulfoxide-induced differentiation in the Friend cell.
Fish as Model Systems
Authors: Powers Dennis A.
Published: October 2006

Fish represent the largest and most diverse group of vertebrates. Their evolutionary position relative to other vertebrates and their ability to adapt to a wide variety of environments make them ideal for studying both organismic and molecular evolution. A number of other characteristics make them excellent experimental models for studies in embryology, neurobiology, endocrinology, environmental biology, and other areas. In fact, they have played a critical role in the development of several of these disciplines. Research techniques that enable scientists to make isogenic lines in a single generation, create and maintain mutants, culture cells, and transfer cloned genes into embryos signal an increasing role for fish as experimental models.
Mutants of Pertussis Toxin Suitable for Vaccine Development
Authors: Pizza Mariagrazia , Covacci Antonio , Bartoloni Antonella , Perugini Maria , Nencioni Luciano , De Magistris Maria Teresa , Villa Luigi , Nucci Daniele , Manetti Roberto , Bugnoli Massimo , Giovannoni Franco , Olivieri Roberto , Barbieri Joseph T. , Sato Hiroko , Rappuoli Rino
Published: October 2006

Immunization with chemically detoxified pertussis toxin can prevent severe whooping cough with an efficacy similar to that of the cellular pertussis vaccine, which normally gives unwanted side effects. To avoid the reversion to toxicity and the loss of immunogenicity that may follow chemical treatment of pertussis toxin, inactive toxins were constructed by genetic manipulation. A number of genetically engineered alleles of the pertussis toxin genes, constructed by replacing either one or two key amino acids within the enzymatically active S1 subunit, were introduced into the chromosome of strains of
Bordetella pertussis
,
B. parapertussis
, and
B. bronchiseptica
. These strains produce mutant pertussis toxin molecules that are nontoxic and immunogenic and that protect mice from the intracerebral challenge with virulent Bordetella pertussis. Such molecules are ideal for the development of new and safer vaccines against whooping cough.
Transgenic Mice as Probes into Complex Systems
Authors: Hanahan Douglas
Published: October 2006

The transfer of genetic information into mouse embryos to stably alter the genetic constitution of mice is affording new insights into and opportunities in a wide variety of biological problems. Higher eukaryotes are composed of many interacting cells and organs. The properties of individual cell systems are often discernible only by studying natural or induced disruptions in their functions. Transgenic mice represent a new form of perturbation analysis whereby the selective expression of novel or altered genes can be used to perturb complex systems in ways that are informative about their development, their functions, and their malfunctions. The utility of this strategy is illustrated by recent research into immunological self-tolerance, oncogenes and cancer, and development.
Fibroblast Growth Factor in the Extracellular Matrix of Dystrophic (mdx) Mouse Muscle
Authors: DiMario J. , Buffinger N. , Yamada S. , Strohman R. C.
Published: October 2006

Polyclonal antibody F547 reacts with a bovine basic fibroblast growth factor (bFGF) and a human recombinant bFGF, but not with bovine acidic fibroblast growth factor. This antibody localized bFGF in the extracellular matrix of mouse skeletal muscle, primarily in the fiber endomysium, which includes the heparin-containing basal lamina. In mdx mouse muscle, which displays persistent regeneration, FGF levels in the extracellular matrix are higher than those in controls. Overabundance of matrix FGF in mdx muscles may be related to an increase in both satellite cell and regenerative activity in the dystrophic muscle and may help explain the benign phenotype of mdx animals compared with the genetically identical human Duchenne muscular dystrophy.
Ectopic Expression of the Serotonin 1c Receptor and the Triggering of Malignant Transformation
Authors: Julius David , Livelli Thomas J. , Jessell Thomas M. , Axel Richard
Published: October 2006

Neurotransmitter receptors are usually restricted to neuronal cells, but the signaling pathways activated by these receptors are widely distributed in both neural and nonneural cells. The functional consequences of activating a brain-specific neurotransmitter receptor, the serotonin 5HT1c receptor, in the unnatural environment of a fibroblast were examined. Introduction of functional 5HT1c receptors into NIH 3T3 cells results, at high frequency, in the generation of transformed foci. Moreover, the generation and maintenance of transformed foci requires continued activation of the serotonin receptor. In addition, the injection of cells derived from transformed foci into nude mice results in the generation of tumors. The serotonin 5HT1c receptor therefore functions as a protooncogene when expressed in NIH 3T3 fibroblasts.
Availability of Metabolic Fuels Controls Estrous Cyclicity of Syrian Hamsters
Authors: Schneider Jill E. , Wade George N.
Published: October 2006

Food deprivation and weight loss inhibit ovulation and estrous behavior in Syrian hamsters. In the present experiments, lean hamsters were more susceptible to starvation-induced anestrus than fat hamsters. However, anestrus was not caused by changes in any dimension of body size per se, but instead by the availability of metabolic fuels. Simultaneous pharmacological blockade of both fatty acid oxidation and glycolysis inhibited reproduction, but, as long as one of these metabolic pathways could be used, estrous cycles continued. Thus, reproduction in female Syrian hamsters is sensitive to the general availability of oxidizable metabolic fuels.
Effect of Serotonergic Afferents on Quantal Release at Central Inhibitory Synapses
Authors: Mintz Isabelle , Gotow Takahiro , Triller Antoine , Korn Henri
Published: October 2006

Although most examples of modulation of synaptic transmission have been obtained from excitatory rather than from inhibitory connections, serotonin (5HT) is now shown to cause a presynaptic facilitation of release of the inhibitory neurotransmitter glycine. Brief local injections of this amine, or application of a 5HT uptake blocker, produce a long-lasting enhancement of both spontaneous and evoked inhibitory currents in the teleost Mauthner cell. Quantal analysis showed that the probability of release is increased. Focal recording indicated that 5HT acts directly on the inhibitory terminals, possibly reducing potassium conductances. Double staining with specific antibodies demonstrated a morphological substrate for this effect. Nerve endings that contain 5HT contact inhibitory terminals directly apposed to postsynaptic glycine receptors.
Neural Cadherin: Role in Selective Cell-Cell Adhesion
Authors: Miyatani Seiji , Shimamura Kenji , Hatta Masayuki , Nagafuchi Akira , Nose Akinao , Matsunaga Mayumi , Hatta Kohei , Takeichi Masatoshi
Published: October 2006

Cadherins are a family of Ca
2+
-dependent intercellular adhesion molecules. Complementary DNAs encoding mouse neural cadherin (N-cadherin) were cloned, and the cell binding specificity of this molecule was examined. Mouse N-cadherin shows 92 percent similarity in amino acid sequence to the chicken homolog, while it shows 49 percent and 43 percent similarity to epithelial cadherin and to placental cadherin of the same species, respectively. In cell binding assays, mouse N-cadherin did not cross-react with other mouse cadherins, but it did cross-react with chicken N-cadherin. The results indicate that each cadherin type confers distinct adhesive specificities on different cells, and also that the specificity of N-cadherin is conserved between mammalian and avian cells.
Influence of Interior Packing and Hydrophobicity on the Stability of a Protein
Authors: Sandberg Warren S. , Terwilliger Thomas C.
Published: October 2006

Protein interiors contain many tightly packed apolar atoms in a nearly crystalline state. Both shielding of apolar atoms from solvent and efficient interior packing arrangements affect protein stability, but their relative importance is unclear. To separate these effects, the stabilities of wild-type and mutant gene V proteins from bacteriophage fl were studied by measuring resistance to denaturation. The effects of subtle interior packing changes, both separate from and combined with changes in buried side chain hydrophobicity, were measured. For the interior apolar-to-apolar substitutions studied, the two effects were of the same magnitude and alteration of packing without accompanying hydrophobicity changes substantially destabilized the protein.
Identification of an AUUUA-Specific Messenger RNA Binding Protein
Authors: Malter James S.
Published: October 2006

An important control point in gene expression is at the level of messenger RNA (mRNA) stability. The mRNAs of certain regulatory cellular proteins such as oncogenes, cytokines, lymphokines, and transcriptional activators are extremely labile. These messages share a common AUUUA pentamer in their 3′ untranslated region, which confers cytoplasmic instability. A cytosolic protein was identified that binds specifically to RNA molecules containing four reiterations of the AUUUA structural element. This protein consists of three subunits and binds rapidly to AUUUA-containing RNA. Such protein-RNA complexes are resistant to the actions of denaturing and reducing agents, demonstrating very stable binding. The time course, stability, and specificity of the protein-AUUUA interaction suggests the possibility that the formation of this complex may target susceptible mRNA for rapid cytoplasmic degradation.
Rapid Stimulation of Diacylglycerol Production in
Xenopus
Oocytes by Microinjection of H-
ras
p21
Authors: Lacal Juan Carlos , de la Peña Pilar , Moscat Jorge , Garcia-Barreno Pedro , Anderson Paul S. , Aaronson Stuart A.
Published: October 2006

The p21 products of
ras
proto-oncogenes are thought to be important components in pathways regulating normal cell proliferation and differentiation. These proteins acquire transforming properties as a result of activating lesions that convert
ras
genes to oncogenes in a wide array of malignancies. In
Xenopus laevis
oocytes, microinjection of transforming
ras
p21 is a potent inducer of maturation, whereas microinjection of a monoclonal antibody to
ras
p21 inhibits normal maturation induced by hormones. The phosphoinositide pathway is a ubiquitous system that appears to play a key role in diverse cellular functions. By use of the
Xenopus
oocyte system, it was possible to quantitate the effects of
ras
p21 microinjection on individual components of the phosphoinositide pathway. Within 20 minutes of microinjection, levels of phosphatidylinositol 4,5-bisphosphate, inositol 1-phosphate, and inositol bisphosphate increased 1.5- to 2-fold. The most striking effects were on diacylglycerol, which increased 5-fold under the same conditions. In contrast, the normal
ras
p21 protein induced no detectable alteration in any of the metabolites analyzed. The earliest effects of the transforming p21 on phosphoinositol turnover were observable within 2 minutes, implying a very rapid effect of
ras
p21 on the enzymes involved in phospholipid metabolism.
Mitogenesis in Response to PDGF and Bombesin Abolished by Microinjection of Antibody to PIP
2
Authors: Matuoka Koozi , Fukami Kiyoko , Nakanishi Osamu , Kawai Sadaaki , Takenawa Tadaomi
Published: October 2006

The turnover of phosphatidylinositol 4,5-bisphosphate (PIP
2
) is believed to constitute a crucial step in the signaling pathways for stimulation of cells by a variety of bioactive substances, including mitogens, but decisive evidence for the idea has not been obtained. In the present study, a monoclonal antibody to PIP
2
was microinjected into the cytoplasm of NIH 3T3 cells before or after exposure to mitogens. The antibody completely abolished nuclear labeling with [
3
H]thymidine induced by platelet-derived growth factor and bombesin, but not by fibroblast growth factor, epidermal growth factor, insulin, or serum. The findings strongly suggest that PIP
2
breakdown is crucial in the elicitation and sustaining of cell proliferation induced by some types of mitogens such as platelet-derived growth factor and bombesin.
A Persistent Untranslated Sequence Within Bacteriophage T4 DNA Topoisomerase Gene
60
Authors: Huang Wai Mun , Ao Shi-Zhou , Casjens Sherwood , Orlandi Richard , Zeikus Regina , Weiss Robert , Winge Dennis , Fang Mei
Published: October 2006

A 50-nucleotide untranslated region is shown to be present within the coding sequence of Escherichia coli bacteriophage T4 gene 60, which encodes one of the subunits for its type II DNA topoisomerase. This interruption is part of the transcribed messenger RNA and appears not to be removed before translation. Thus, the usual colinearity between messenger RNA and the encoded protein sequence apparently does not exist in this case. The interruption is bracketed by a direct repeat of five base pairs. A mechanism is proposed in which folding of the untranslated region brings together codons separated by the interruption so that the elongating ribosome may skip the 50 nucleotides during translation. The alternative possibility, that the protein is efficiently translated from a very minor and undetectable form of processed messenger RNA, seems unlikely, but has not been completely ruled out.
Intracellular Injection of cAMP Induces a Long-Term Reduction of Neuronal K
+
Currents
Authors: Scholz Kenneth P. , Byrne John H.
Published: October 2006

Intracellular signals that trigger long-term (24-hour) changes in membrane currents in identified neurons of
Aplysia
have been examined in order to understand the cellular mechanisms underlying long-term sensitization. Adenosine 3′,5′-monophosphate (cAMP) was directly injected into individual sensory neurons to mimic the effects of sensitization training at the single cell level. Potassium currents of these cells were reduced 24 hours after injection of cAMP; these currents were similar to those reduced 24 hours after behavioral sensitization. These results suggest that cAMP is part of the intracellular signal that induces long-term sensitization in
Aplysia
.
NMDA Receptor Losses in Putamen from Patients with Huntington's Disease
Authors: Young Anne B. , Greenamyre J. Timothy , Hollingsworth Zane , Albin Roger , D'Amato Constance , Shoulson Ira , Penney John B.
Published: October 2006

N
-Methyl-D-aspartate (NMDA), phencyclidine (PCP), and quisqualate receptor binding were compared to benzodiazepine, γ-aminobutyric acid (GABA), and muscarinic cholinergic receptor binding in the putamen and cerebral cortex of individuals with Huntington's disease (HD). NMDA receptor binding was reduced by 93 percent in putamen from HD brains compared to binding in normal brains. Quisqualate and PCP receptor binding were reduced by 67 percent, and the binding to other receptors was reduced by 55 percent or less. Binding to these receptors in the cerebral cortex was unchanged in HD brains. The results support the hypothesis that NMDA receptor-mediated neurotoxicity plays a role in the pathophysiology of Huntington's disease.
Protein Translocation Across Membranes
Authors: Verner Keith , Schatz Gottfried
Published: October 2006

Many newly synthesized proteins must be translocated across a membrane to reach their final destinations. Translocation requires a signal on the protein itself, a loose conformation of the protein, energy, and receptor-like components in the cytosol and on the target membrane.
Phenotypic Diversity Mediated by the Maize Transposable Elements
Ac
and
Spm
Authors: Wessler Susan R.
Published: October 2006

Mutations caused by the insertion of members of the Ac or
Spm
family of transposable elements result in a great diversity of phenotypes. With the cloning of the mutant genes and the characterization of their products, the mechanisms underlying phenotypic diversity are being deciphered. These mechanisms include (i) imprecise excision of transposable elements, which can result in the addition of amino acids to proteins; (ii) DNA methylation, which has been correlated with the activity of the element; (iii) transposase-mediated deletions within elements, which can inactivate an element or lead to a new unstable phenotype; and (iv) removal of transcribed elements from RNA, which can facilitate gene expression despite the insertion of elements into exons. An understanding of the behavior of the maize elements has provided clues to the function of cryptic elements in all maize genomes.
Inositol 1,3,4,5-Tetrakisphosphate Induces Ca
2+
Sequestration in Rat Liver Cells
Authors: Hill Timothy D. , Dean Nicholas M. , Boynton Alton L.
Published: October 2006

Inositol 1,4,5-trisphosphate [I(1,4,5)P
3
] is a second messenger generated along with diacylglycerol upon the binding of various physiological agents with their cell surface receptors. I(1,4,5)P
3
mobilizes Ca
2+
from intracellular storage sites through a receptor-coupled mechanism, and the subsequent increased intracellular free calcium ion concentration ([Ca
2+
]
i
) activates a multitude of cellular responses. Electropermeabilized neoplastic rat liver epithelial (261B) cells were used to study Ca
2+
sequestration, a process that reverses the elevated [Ca
2+
]
i
to resting levels and replenishes intracellular Ca
2+
pools. Although I(1,4,5)P
3
-mobilized Ca
2+
is readily sequestered into storage pools by the action of Ca
2+
-adenosine triphosphatases, Ca
2+
mobilized by addition of the nonmetabolized inositol trisphosphate isomer I(2,4,5)P
3
is not sequestered, suggesting that metabolism is necessary to eliminate the stimulus for Ca
2+
release. Several inositol phosphate compounds were examined for their ability to lower the buffer [Ca
2+
] to determine if a specific I(1,4,5)P
3
metabolite might be involved in stimulating Ca
2+
sequestration; of these, I(1,3,4,5)P
4
alone was found to induce Ca
2+
sequestration, demonstrating a physiological role for this inositol trisphosphate metabolite.
Mechanism of Transmitter Release: Voltage Hypothesis and Calcium Hypothesis
Authors: Zucker Robert S. , Landò Luca
Published: October 2006

The calcium hypothesis of synaptic transmission has been challenged by experimental results using the crayfish neuromuscular junction that suggest that presynaptic depolarization can trigger transmitter release directly without calcium influx. Results from electrophysiological experiments using the same preparation do not support this voltage hypothesis, but are consistent with the calcium hypothesis. Voltage may modulate, but not elicit, transmitter release.
Differences in Adrenergic Recognition by Pancreatic A and B Cells
Authors: Schuit F. C. , Pipeleers D. G.
Published: October 2006

The adrenergic control of glucose homeostasis is mediated in part through variations in the release of pancreatic hormones. In this study, purified pancreatic A and B cells were used to identify the recognition and messenger units involved in the adrenergic regulation of glucagon and insulin release. Catecholamines induced β-adrenergic receptor activity in A cells and α
2
-adrenergic receptor activity in B cells. The two recognition units provoked opposite variations in the production of cellular cyclic adenosine monophosphate, the β-adrenergic unit enhancing the nucleotide's permissive effect on amino acid-induced glucagon release and the α
2
-adrenergic unit inhibiting that upon glucose-induced insulin release. In both cell types, catecholamines interact powerfully with the synergistic control of hormone release by nutrient- and (neuro)hormone-driven messenger systems.
Identification of a T3-Associated γδ T Cell Receptor on Thy-1
+
Dendritic Epidermal Cell Lines
Authors: Koning Frits , Stingl Georg , Yokoyama Wayne M. , Yamada Hidekazu , Maloy W. Lee , Tschachler Erwin , Shevach Ethan M. , Coligan John E.
Published: October 2006

The murine epidermis contains a subpopulation of bone marrow-derived lymphocytes that have a dendritic morphology and that express Thy-1 and T3 cell-surface antigens but not other markers (L3T4 or Lyt-2) characteristic of mature peripheral T lymphocytes. An alternative type of T cell receptor was earlier identified on a subpopulation of murine thymocytes with a similar phenotype (T3
+
, L3T4
-
, Lyt-2
-
), but not on peripheral murine T lymphocytes. Two independently derived Thy-1
+
, L3T4
-
, and Lyt-2
-
dendritic cell lines of epidermal origin that express a T3-associated disulfide-linked heterodimer composed of a 34-kilodalton γ-chain and 46-kilodalton partner (the δ chain) have now been identified. Analysis of
N
-linked glycosylation revealed that this receptor is similar to that detected on thymocytes. These results demonstrate that Thy-1
+
dendritic epidermal cell lines can express γδ T cell receptors in vitro and suggest that Thy-1
+
dendritic epidermal cells express such receptors in vivo. The localization of these γδ T cell receptor-expressing cells in the epidermis may be of importance for understanding the function of these receptors.
Limited Immunological Recognition of Critical Malaria Vaccine Candidate Antigens
Authors: Good Michael F. , Miller Louis H. , Kumar Sanjai , Quakyi Isabella A. , Keister David , Adams John H. , Moss Bernard , Berzofsky Jay A. , Carter Richard
Published: October 2006

Current vaccine development strategies for malaria depend on widespread immunological responsiveness to candidate antigens such as the zygote surface antigens and the sporozoite coat protein, the circumsporozoite (CS) protein. Since immunological responsiveness is controlled mainly by genes mapping within the major histocompatibility complex (MHC), the humoral immune response to the zygote surface antigens and the cytotoxic T lymphocyte (CTL) response to the CS protein were examined in MHC-disparate congenic mouse strains. Only two of six strains responded to the 230-kilodalton zygote surface antigen and another two strains responded to the 48/45-kilodalton surface antigen. From two mouse strains, expressing between them five different class I MHC molecules, there was recognition of only a single CTL epitope from the CS protein, which was from a polymorphic segment of the molecule. The restricted CTL response to this protein parallels the restricted antibody response to this protein observed in humans and mice. These findings suggest that subunit malaria vaccines now being developed may be ineffective.
Prevalence and Patterns of Same-Gender Sexual Contact Among Men
Authors: Fay Robert E. , Turner Charles F. , Klassen Albert D. , Gagnon John H.
Published: October 2006

The prevalence and patterns of same-gender sexual contact among men are key components of models of the spread of HIV infection and AIDS in the U.S. population. Previous estimates by Kinsey
et al.
from data collected between 1938 and 1948 have been widely criticized for inadequacies of sample design. New lower-bound estimates of prevalence developed from data from a national sample survey conducted in 1970 indicate that minimums of 20.3 percent of adult men in the United States in 1970 had sexual contact to orgasm with another man at some time in life; 6.7 percent had such contact after age 19; and between 1.6 and 2.0 percent had such contact within the previous year. Although these estimates incorporate adjustments for missing data, the likelihood of underreporting suggests that these estimates might be lower bounds on the prevalence of same-gender sex among men. Two sets of alternative estimates are derived to assess the sensitivity of these estimates to the assumptions made in imputing values to missing data. Detailed estimates are presented by frequency of contact, age, education, and marital status; and supporting estimates are derived from a 1988 national survey. Data from both the 1970 and 1988 surveys indicate that never-married men are more likely than other men to have had same-gender sexual contacts within the last year. The 1970 survey also indicates, however, that approximately half the men estimated to have such contacts are found among the more numerous population of currently or previously married men.
Physiological Constraint on Feeding Behavior: Intestinal Membrane Disaccharidases of the Starling
Authors: Martinez del Rio Carlos , Stevens Bruce R.
Published: October 2006

Animals clearly choose what they eat and can even choose among chemically different sugars. The physiological and biochemical mechanisms that constrain feeding choices are largely unknown. In this study, European starlings (
Sturnus vulgaris
) preferred mixture solutions of D-glucose plus D-fructose to equimolar (double molar caloric value) solutions of sucrose. Intubation feeding of sucrose did not increase blood glucose levels. Sucrose is a useless energy source for these birds because they lack a single digestive enzyme (sucrase) on the small intestinal brush border membrane. However, the membranes possessed separate maltase and isomaltase disaccharidases. This expression pattern and expression patterns of membrane disaccharidases among mammals suggest a role for intestinal enzymes in the coevolutionary interactions between vertebrates and their plant food sources.
Sindbis Virus: An Efficient, Broad Host Range Vector for Gene Expression in Animal Cells
Authors: Xiong Cheng , Levis Robin , Shen Ping , Schlesinger Sondra , Rice Charles M. , Huang Henry V.
Published: October 2006

Sindbis virus, an enveloped virus with a single-stranded RNA genome, was engineered to express a bacterial protein, chloramphenicol acetyltransferase (CAT), in cultured insect, avian, and mammalian cells. The vectors were self-replicating and gene expression was efficient and rapid; up to 10
8
CAT polypeptides were produced per infected cell in 16 to 20 hours. CAT expression could be made temperature-sensitive by means of a derivative that incorporated a temperature-sensitive mutation in viral RNA synthesis. Vector genomic RNAs were packaged into infectious particles when Sindbis helper virus was used to supply virion structural proteins. The vector RNAs were stable to at least seven cycles of infection. The expression of CAT increased about 10
3
-fold, despite a 10
15
-fold dilution during the passaging. Sindbis virus vectors should prove useful for expressing large quantities of gene products in a variety of animal cells.
Imaging Crystals, Polymers, and Processes in Water with the Atomic Force Microscope
Authors: Drake B. , Prater C. B. , Weisenhorn A. L. , Gould S. A. C. , Albrecht T. R. , Quate C. F. , Cannell D. S. , Hansma H. G. , Hansma P. K.
Published: October 2006

The atomic force microscope (AFM) can be used to image the surface of both conductors and nonconductors even if they are covered with water or aqueous solutions. An AFM was used that combines microfabricated cantilevers with a previously described optical lever system to monitor deflection. Images of mica demonstrate that atomic resolution is possible on rigid materials, thus opening the possibility of atomic-scale corrosion experiments on nonconductors. Images of polyalanine, an amino acid polymer, show the potential of the AFM for revealing the structure of molecules important in biology and medicine. Finally, a series of ten images of the polymerization of fibrin, the basic component of blood clots, illustrate the potential of the AFM for revealing subtle details of biological processes as they occur in real time.
Major Enhancement of the Affinity of an Enzyme for a Transition-State Analog by a Single Hydroxyl Group
Authors: Kati Warren M. , Wolfenden Richard
Published: October 2006

The compound 1,6-dihydropurine ribonucleoside, prepared by reduction of nebularine in the presence of ultraviolet light, is bound by adenosine deaminase approximately 10(8)-fold less tightly than 6-hydroxy-1,6-dihydropurine ribonucleoside, a nearly ideal transition-state analog. This difference in affinities, which is associated with the presence of a single hydroxyl group in the second compound, suggests the degree to which one or a few hydrogen bonds may stabilize the transition state in an enzyme reaction of this type.
Conformations of Signal Peptides Induced by Lipids Suggest Initial Steps in Protein Export
Authors: Briggs Martha S. , Cornell Donald G. , Dluhy Richard A. , Gierasch Lila M.
Published: October 2006

Despite the requirement for a functional signal sequence in protein export, little is known of the conformational properties and membrane interactions of these highly hydrophobic amino terminal extensions on nearly all exported proteins. The
Escherichia coli
λ phage receptor signal sequence was studied in phospholipid monolayers by circular dichroism and Fourier transform infrared spectroscopy; the signal peptide was shown to prefer an α-helical conformation when inserted into the lipid phase. However, interaction with the lipid surface without insertion induced the signal sequence, which is unstructured in bulk aqueous solution, to adopt a β structure. These observations are combined in a model for the initial steps in signal sequence-membrane interaction in vivo.
Characterization of Long Terminal Repeat Sequences of HTLV-III
Authors: Starcich Bruno , Ratner Lee , Josephs Steven F. , Okamoto Takashi , Gallo Robert C. , Wong-Staal Flossie
Published: October 2006

The nucleotide sequence of the long terminal repeat sequence (LTR) of the human T-cell leukemia (lymphotropic) virus type III (HTLV-III) was determined. This virus is associated etiologically with the acquired immune deficiency syndrome. The LTR was found to be 634 base pairs in length with U3, R, and U5 regions of 453, 98, and 83 bp, respectively. The proviral DNA is flanked by a 7-base-pair direct repeat. The promoter and polyadenylation signals are situated 27 and 24 base pairs upstream from the respective transcriptional initiation and polyadenylation sites. The primer binding site is complementary to transfer RNA-lysine. The LTR of HTLV-III, like that of HTLV-I, showed a limited homology to enhancer-like sequences within two genes expressed specifically in T lymphocytes, T-cell growth factor, and γ-interferon. Structural comparisons revealed that the LTR of HTLV-III is distantly related to those of HTLV-I, HTLV-II, and bovine leukemia virus.
A General Method for Saturation Mutagenesis of Cloned DNA Fragments
Authors: Myers Richard M. , Lerman Leonard S. , Maniatis Tom
Published: October 2006

A new procedure for generating and isolating random single-base substitutions in cloned DNA fragments is presented. The mutations are generated by treatment of single-stranded DNA with various chemicals, followed by the synthesis of the complementary strand with reverse transcriptase. Misincorporation frequently occurs when the enzyme encounters a damaged base in the mutagenized template DNA. The resulting duplex DNA fragments containing random single-base substitutions are cloned, amplified as a population, and isolated from wild-type DNA by preparative denaturing gradient gel electrophoresis. The physical separation of mutant DNA fragments makes it possible to isolate and characterize large numbers of site-directed single-base substitutions in the absence of a phenotypic selection. This procedure should be generally applicable to the fine-structure genetic analysis of regulatory and protein-coding sequences.
Genomic Diversity of Human T-Lymphotropic Virus Type III (HTLV-III)
Authors: Wong-Staal Flossie , Shaw George M. , Hahn Beatrice H. , Salahuddin S. Zaki , Popovic Mikulas , Markham Phillip , Redfield Robert , Gallo Robert C.
Published: October 2006

The DNA genomes of human T-lymphotropic virus type III (HTLV-III) isolated from 18 individuals with AIDS or who were at risk for AIDS were evaluated for evidence of variation. Although all of the 18 viral DNA's hybridized throughout their entire genomes to a full-length cloned probe of the original HTLV-III isolate, each of the 18 isolates showed a different restriction enzyme pattern. The number of restriction site differences between isolates ranged from only 1 site in 23 to at least 16 sites in 31. No particular viral genotype was associated with a particular disease state and 2 of the 18 patients had evidence of concurrent infection by more than one viral genotype. Propagation of three different viral isolates in vitro for up to 9 months did not lead to detectable changes in their restriction patterns. These findings indicate that different isolates of HTLV-III comprise a spectrum of highly related but distinguishable viruses and have important implications regarding the pathogenicity of HTLV-III and attempts to develop effective diagnostic, therapeutic, and preventive measures for this virus.
Three-Dimensional Structure of Poliovirus at 2.9 Å Resolution
Authors: Hogle J. M. , Chow M. , Filman D. J.
Published: October 2006

The three-dimensional structure of poliovirus has been determined at 2.9 Å resolution by x-ray crystallographic methods. Each of the three major capsid proteins (VP1, VP2, and VP3) contains a "core" consisting of an eight-stranded antiparallel beta barrel with two flanking helices. The arrangement of beta strands and helices is structurally similar and topologically identical to the folding pattern of the capsid proteins of several icosahedral plant viruses. In each of the major capsid proteins, the "connecting loops" and NH
2
- and COOH-terminal extensions are structurally dissimilar. The packing of the subunit "cores" to form the virion shell is reminiscent of the packing in the
T
= 3 plant viruses, but is significantly different in detail. Differences in the orientations of the subunits cause dissimilar contacts at protein-protein interfaces, and are also responsible for two major surface features of the poliovirion: prominent peaks at the fivefold and threefold axes of the particle. The positions and interactions of the NH
2
- and COOH-terminal strands of the capsid proteins have important implications for virion assembly. Several of the "connecting loops" and COOH-terminal strands form prominent radial projections which are the antigenic sites of the virion.
Identification of the Protein Encoded by the E6 Transforming Gene of Bovine Papillomavirus
Authors: Androphy Elliot J. , Schiller John T. , Lowy Douglas R.
Published: October 2006

Papillomaviruses (PV) contain several conserved genes that may encode nonstructural proteins; however, none of these predicted gene products have been identified. Papillomavirus E6 genes are retained and expressed as RNA in PV-associated human and animal carcinomas and cell lines. This suggests that the E6 gene product may be important in the maintenance of the malignant phenotype. The E6 open reading frame of the bovine papillomavirus (BPV) genome has been identified as one of two BPV genes that can independently transform mouse cells in vitro. A polypeptide encoded by this region of BPV was produced in a bacterial expression vector and used to raise antisera. The antisera specifically immunoprecipitated the predicted 15.5-kilodalton BPV E6 protein from cells transformed by the E6 gene. The E6 protein was identified in both the nuclear and membrane fractions of these transformed cells.
Identification of HTLV-III/LAV
sor
Gene Product and Detection of Antibodies in Human Sera
Authors: Kan Nancy C. , Franchini Genoveffa , Wong-Staal Flossie , DuBois Garrett C. , Robey W. Gerard , Lautenberger James A. , Papas Takis S.
Published: October 2006

The nucleotide sequence of the genome of HTLV-III, the infectious agent etiologically associated with the acquired immune deficiency syndrome, predicts a small open reading frame, termed
sor
, located between the
pol
and
env
genes. A DNA segment containing 82 percent of the
sor
region was inserted into a prokaryotic expression vector, pJL6, to determine whether
sor
encodes a viral protein and to gain some insight into its possible function. The bacterially synthesized
sor
protein reacted with sera from individuals infected with HTLV-III, indicating that
sor
is expressed as a protein product or products that are immunogenic in vivo. Antibodies to the purified, bacterially synthesized
sor
protein were found to react specifically with the same protein and also with a protein of molecular weight 23,000 (23K) in HTLV-III-infected H9 cell extracts. The 23K protein comigrated with a protein immunoprecipitated by the serum of a hemophiliac patient with antibodies to HTLV-III, suggesting that this protein is probably the
sor
gene product.
Neutralization of the AIDS Retrovirus by Antibodies to a Recombinant Envelope Glycoprotein
Authors: Lasky Laurence A. , Groopman Jerome E. , Fennie Christopher W. , Benz Patricia M. , Capon Daniel J. , Dowbenko Donald J. , Nakamura Gerald R. , Nunes Wylla M. , Renz Mark E. , Berman Phillip W.
Published: October 2006

Mammalian cell lines have been engineered to produce a secreted form of the AIDS retrovirus envelope glycoprotein. The recombinant protein has been isolated from growth-conditioned culture media and used to immunize animals. Antibodies directed against the recombinant molecule were found to react with the envelope glycoprotein produced in virus-infected cells. Furthermore, these antibodies were able to directly inactivate the AIDS retrovirus in a neutralization assay in vitro. The expression system reported here should provide sufficient quantities of the AIDS retrovirus envelope protein for biological and vaccination studies.
Nude Mouse: A New Experimental Model for
Pneumocystis carinii
Infection
Authors: Walzer Peter D. , Schnelle Vera , Armstrong Donald , Rosen P. Peter
Published: October 2006

Experimental infection with both human- and rat-derived
Pneumocystis carinii
has been produced in nude mice by intrapulmonary injection of lung homogenates that contained
P. carinii
and by environmental transmission. Most infected mice did not appear ill, and their lungs exhibited a mild and nonspecific inflammatory response. Thus,
P. carinii
can be transmitted from one animal species to another, and this result suggests that a defect in thymic-dependent lymphocytes is important in the development of the infection. Experimental work with
P. carinii
in the nude mouse should be performed in isolators because of the communicability of the organism.
Diminished Response of Werner's Syndrome Fibroblasts to Growth Factors PDGF and FGF
Authors: Bauer Eugene A. , Silverman Neil , Busiek Donald F. , Kronberger Annemarie , Deuel Thomas F.
Published: October 2006

Patients with Werner's syndrome, an autosomal recessive disorder, undergo an accelerated aging process that leads to premature death. Fibroblasts from such patients typically grow poorly in culture. Here it is shown that fibroblasts from a patient with Werner's syndrome have a markedly attenuated mitogenic response to platelet-derived growth factor (PDGF) and fibroblast growth factor (FGF). In contrast, they have a full mitogenic response to fetal bovine serum. Both PDGF binding and receptor numbers per cell are unaltered. The Werner's syndrome cells express high constitutive levels of collagenase in vitro. Although PDGF enhances collagenase expression through increased levels of hybridizable collagenase messenger RNA in normal skin fibroblasts, no induction of collagenase occurs in the Werner's syndrome fibroblasts. Moreover, the failure to respond to this agonist effect of PDGF is not restored by fetal bovine serum. The data suggest that failure of one or more PDGF-mediated pathways in Werner's syndrome cells may contribute to the phenotypic expression of the disorder.
Ouabain Resistance Conferred by Expression of the cDNA for a Murine Na
+
, K
+
-ATPase α Subunit
Authors: Kent Rachel B. , Emanuel Janet Rettig , Ben Neriah Yinon , Levenson Robert , Housman David E.
Published: October 2006

The molecular basis for the marked difference between primate and rodent cells in sensitivity to the cardiac glycoside ouabain has been established by genetic techniques. A complementary DNA encoding the entire α
1
subunit of the mouse Na
+
- and K
+
-dependent adenosine triphosphatase (ATPase) was inserted into the expression vector pSV2. This engineered DNA molecule confers resistance against 10
-4
M
ouabain to monkey CV-1 cells. Deletion of sequences encoding the carboxyl terminus of the α
1
subunit abolish the activity of the complementary DNA. The ability to assay the biological activity of this ATPase in a transfection protocol permits the application of molecular genetic techniques to the analysis of structure-function relationships for the enzyme that establishes the internal Na
+
/K
+
environment of most animal cells. The full-length α
1
subunit complementary DNA will also be useful as a dominant selectable marker for somatic cell genetic studies utilizing ouabain-sensitive cells.