bluuebunny/crossref_metadata_2025 huggingface dataset:
Differential amplitude contrast in acoustic microscopy
Authors: Nikoonahad M.
Published: July 2002

A differential amplitude contrast scanning acoustic microscope is described. The operation of this system resides on a two-beam acoustic lens which produces two adjacent spots at its focal plane. The signals received from these two foci are first amplitude demodulated and then electronically subtracted from each other, resulting in a differential amplitude imaging signal. Experiments at 10 MHz are described and illustrated by a number of images.
Dynamic sensitivity and thermal noise analysis of a magnetoelastic amorphous metal low-frequency magnetometer
Authors: Mermelstein M. D. , Dandridge A.
Published: July 2002

The ferromagnetic susceptibility of a magnetoelastic amorphous metal ribbon is determined from the coupled equations of motion for the magnetization and strain modes. This analysis is used to calculate the dynamic sensitivity and field equivalent noise floor of a metallic glass low-frequency magnetometer. Two principal noise sources are considered: the thermally induced magnetization fluctuations and the Johnson noise of the pick-up coil. The magnetometer exhibits a calculated minimum detectable field of ∼0.1 pT/(Hz)1/2 for room temperature operation at a resonance frequency of 22 kHz and 103 turn pick-up coil having a 200-Ω resistance. The fundamental material limit is estimated to be ∼5 fT/(Hz)1/2.
Direct writing onto Si by electron beam stimulated etching
Authors: Matsui Shinji , Mori Katsumi
Published: July 2002

Direct writing onto Si has been demonstrated by electron beam induced surface reaction using a XeF2 source. The electron beam stimulated etched depth for Si(100) is proportional to the electron dose. Etch depth by electron beam stimulated etching is 500 nm at 10 kV accelerating voltage, 4×10−3 C/cm2 dose, and 5 mTorr XeF2 gas pressure. An enormously high etching yield of about 100 Si atoms per electron has been observed for electron stimulated etching using the XeF2 source. A 0.5-μm linewidth pattern has been fabricated at a 4×10−3 C/cm2 dose.
Characterization of short-range leakage currents in undoped polycrystalline Si by means of capacitance-voltage measurement
Authors: Alpern Y. , Shappir J.
Published: July 2002

Metal-oxide-semiconductor capacitors with undoped polycrystalline Si (polysilicon) electrodes were studied and a model was developed to explain the voltage and frequency dependence of the capacitance and serial resistance. The model assumes random distribution of leaky paths in the polycrystalline Si layer which supply the charge to the polysilicon-oxide interface.
Thin films of amorphous MoO3 as a negative resist
Authors: Gupta P. K. , Chopra K. L.
Published: July 2002

Lithographic properties of amorphous MoO3 films exposed to a glow discharge hydrogen plasma have been investigated. It has been observed that the etching rate of an exposed film in alkaline solution is lower compared to an unexposed one, giving rise to a negative tone behavior of the material. The etching characteristics as a function of exposure time and substrate temperature (during exposure) and their correlation with optical transmission have been studied. The contrast (γ) obtained is 4.2.
Ion implantation and annealing of undoped (Al,Ga)As/GaAs heterostructures
Authors: Baratte H. , Jackson T. N. , Solomon P. M. , LaTulipe D. C. , Frank D. J. , Moore J. S.
Published: July 2002

Electrical measurements of n+-GaAs/π-(Al,Ga)As/π-GaAs semiconductor-insulator-semiconductor (SIS) heterostructure capacitors and field-effect transistors (FET’s) show that the (Al,Ga)As/GaAs heterojunction abruptness is well preserved for an arsine flash anneal of 1 s at temperatures up to ∼900 °C. The heterostructure stability is also preserved for a low-dose silicon implant across the (Al,Ga)As/GaAs heterojunction and subsequent annealing. Arsenic overpressure is found to be necessary, even for short time annealing, to prevent excessive As loss from a GaAs or (Al,Ga)As surface. High mobility enhance–deplete heterostructure SISFET’s with sharp current versus voltage (I-V) turn-on characteristics have been fabricated using ion implantation and arsine flash anneal.
Surface enhancement of the second harmonic generation on the GaAs-Al interface by the s-polarized fundamental wave
Authors: Chen Zhenghao , Cui Dafu , Zhou Yueliang , Lu Huibin , Yang Guozhen , Gu Shijie
Published: July 2002

The theoretical and experimental results demonstrate, for the first time, that the enhancement of the reflected surface second harmonic generation on the rough GaAs-Al interface arises from the nonlinear resonant excitation of the harmonic surface polariton mode with s-polarized incident radiation. The experimental results agree quite well with the theoretical analysis. An optimum surface second harmonic enhancement of ∼three orders of magnitude has been obtained.
Tandem transmission characteristics of laser diode optical switches measured by a circular pulse method
Authors: Yoshino Kaoru , Ikeda Masahiro
Published: July 2002

Tandem transmission characteristics of laser diode optical switches have been measured using the circular pulse method. With an input optical signal power level of −18 dBm, output optical signal pulses have been observed to recirculate 50 times without a filter, and more than 80 times with an optical bandpass filter inserted in front of a photodetector.
Intensity oscillations in reflection high-energy electron diffraction during molecular beam epitaxy of Ni on W(110)
Authors: Koziol C. , Lilienkamp G. , Bauer E.
Published: July 2002

Reflection high-energy electron diffraction intensities during molecular beam epitaxy growth of Ni on W(110) were studied. The damping and polar angle dependence of the observed oscillations are discussed. Intensity oscillations during preparation of a Ni/Cu superlattice are also reported.
Standing light wave in front of a silver mirror investigated by photothermal spectroscopy
Authors: Knoll Wolfgang , Coufal Hans J.
Published: July 2002

Photothermal spectra of an isocyanine dye monolayer, separated from a silver mirror by a varying number of cadmium arachidate layers, are recorded with a pyroelectric calorimeter. The spatial dependence of the light intensity in front of the silver mirror is observed. The phase angle of a light wave upon reflection from the silver surface is determined to be 124±5° at a wavelength of 578 nm. The quantum yield for radiationless deexcitation at that wavelength is found to be 33±7%.
Tunnel spectroscopy using titanium metal barriers on p−-Si/p+-Si molecular beam epitaxial films
Authors: Cabanski W. , Schulz M. , Kasper E. , Herzog H. J.
Published: July 2002

Tunnel spectroscopy is employed to analyze electronic and vibrational excitations in Ti/p−-Si/p+-Si structures. The thin p−-Si layer of about 70 Å thickness was grown by molecular beam epitaxy (MBE). The second derivative of the tunneling current through the Ti/p−-Si Schottky barrier is measured at a temperature T=8 K. A series of peaks is observed in the voltage range 0 to ±80 mV. The observed structure is interpreted by inelastic tunneling via phonons. Impurity states of Ga-x(E−Ev=57 meV), Ga+(E−Ev=2 meV), B(E−Ev=46 meV), and B-x(E−Ev=37 meV) in Si can be resolved at the interface of the MBE films. The method may be also useful to analyze interface states at the metal-semiconductor interface.
Formation of buried layers of β-SiC using ion beam synthesis and incoherent lamp annealing
Authors: Reeson K. J. , Hemment P. L. F. , Stoemenos J. , Davis J. , Celler G. E.
Published: July 2002

It is demonstrated that well-defined buried layers of β-SiC can be grown epitaxially within a silicon substrate. This structure is formed by implanting high doses of carbon ions (>3×1017 C+ cm−2) at 200 keV into a (100) single-crystal silicon which is maintained at a temperature of approximately 550 °C. During the subsequent anneal at 1405 °C for 90 min redistribution of the implanted species occurs, enabling the formation of a buried layer of β-SiC overlain by high-quality single-crystal silicon (χmin=4.1%).
Flat-surface buried heterostructure distributed feedback lasers operating in a single longitudinal mode at 1.5 μm with low chirp
Authors: Nilsson Stefan , Tanbun-Ek Tawee , Broberg Björn
Published: July 2002

Distributed feedback lasers emitting in a stable dynamic single mode at 1.5 μm wavelength in a temperature range of more than 50 °C have been developed using the so-called flat-surface buried heterostructure. Threshold currents as low as 14 mA in cw (8 mA in pulse) operating and output powers as high as 20 mW/facet were obtained. By detuning the Bragg wavelength to the shorter wavelength side of the gain peak, and by reducing the confinement factor, a wavelength chirp as a function of modulation current as low as 0.003 nm/mA has been obtained. This value corresponds to a total chirp of 0.1–0.2 nm under normal modulation conditions.
Mode structure of the p-germanium far-infrared laser with and without external mirrors: Single line operation
Authors: Unterrainer K. , Helm M. , Gornik E. , Haller E. E. , Leotin J.
Published: July 2002

The mode structure of p-Ge far-infrared lasers with and without mirrors is investigated. Without external mirrors a multimode spectrum is observed and quantitatively explained in terms of waveguidelike modes. An external resonator drastically reduces the number of oscillating modes. For the first time single line operation is demonstrated in this configuration.
Phase separation kinetics of metastable, highly supersaturated Sn-Bi single crystals
Authors: Fecht H. J. , Tringides M. C.
Published: July 2002

We have utilized differential scanning calorimetry to study decomposition of a large number (≊105) of independent, metastable, highly supersaturated Sn63Bi37 single crystals. Three different growth regimes are observed: first, t1/2 diffusion-controlled growth, followed by a t1/3 regime attributed to Lifshitz–Slyozov coarsening [J. Phys. Chem. Solids 19, 35 (1961)] extended to the case of finite volume fraction, and eventually ‘‘freezing’’ of the growth possibly because of defects. The activation energy of the t1/3 growth is determined to be 0.54±0.05 eV.
Amorphous GdCo: Effect of surface segregation on reading of the magnetization by spin-polarized photoemission
Authors: Bona G. L. , Meier F. , Siegmann H. C. , Gambino R. F.
Published: July 2002

Spin-polarized photoemission can be used to read the surface magnetization direction of perpendicularly magnetized amorphous GdCo films. Effects specific of the photoemission process are observed: (1) surface depolarization by disordered Gd moments in the outermost segregated layers of the film, (2) change of the polarization upon varying the probing depth of the photoelectrons. Both effects are consequences of the inhomogeneous surface composition of amorphous GdCo due to segregation.
Growth of the superconducting phase in ceramic Y1.2Ba0.8CuOy samples
Authors: Wördenweber R. , Krebs H. U. , Gelsdorf F. , Heinemann K. , Sastry G. V. S. , Freyhardt H. C. , Winzer K.
Published: July 2002

Differently prepared samples with the nominal composition Y1.2Ba0.8CuOy are examined via microscopy, energy dispersive x-ray analysis, x-ray diffraction, and measurements of resistivity and susceptibility. Various phases are identified directly. Essentially these are Y2BaCuO5, which forms a matrix with semiconducting and antiferromagnetic properties and YBa2Cu3O7−x, which is present in a dendritic morphology. The dendritic appearance indicates that YBa2Cu3O7−x is formed by nucleation and growth during sintering. Despite the particular growth mechanism of sintered materials a strong analogy exists with dendritic growth during solid-state transformations in metallic alloys.
Oval defects in Ga1−xAlxAs molecular beam epitaxy layers: A Raman scattering and photoluminescence combined study
Authors: Sapriel J. , Chavignon J. , Alexandre F.
Published: July 2002

Oval defects in Ga1−xAlxAs molecular beam epitaxy layers are characterized by spatially resolved Raman and photoluminescence studies performed at room temperature with a Raman microprobe. Changes in the crystallographic orientation and chemical composition are evidenced by Raman scattering. The modification of the Ga concentration which occurs inside the oval defect is confirmed by photoluminescence investigation.
Suppression of lateral Ti silicide growth by ion beam mixing and rapid thermal annealing
Authors: Ku Y. H. , Lee S. K. , Shih D. K. , Kwong D. L. , Lee C-O , Yeargain J. R.
Published: July 2002

One of the most important issues in the self-aligned silicide technology has been lateral silicide formation over the sidewall oxide spacers. In this work, the lateral silicide growth has been considerably suppressed by the use of ion beam mixing and rapid thermal annealing. Metal-oxide-semiconductor transistors fabricated using this technology show good electrical characteristics with negligible conduction between gate and source/drain electrodes.
Coherent precipitation of silicon nitride in silicon
Authors: Kaushik V. S. , Datye A. K. , Kendall D. L. , Martinez-Tovar B. , Myers D. R.
Published: July 2002

Coherent growth of α-Si3N4 precipitates is observed in a silicon matrix after implantation of 150 keV N+ at a dose of 1×1018/cm2 into (110) silicon. The near-channeling conditions lead to a band of discrete precipitates, 0.5 μm below the continuous, polycrystalline buried nitride layer. No misfit dislocations or strain contrast were observed in the silicon matrix despite a 10% lattice mismatch along the Si3 N4 [0001] direction and a 1% mismatch along directions perpendicular to [0001]. The mismatch appears to be accommodated entirely within the precipitate by a mosaic structure consisting of single-crystal subunits, coherent with Si at the Si3 N4 (0001)/Si{111} interface, but incoherent perpendicular to these planes.
Room-temperature switching and negative differential resistance in the heterostructure hot-electron diode
Authors: Higman T. K. , Miller L. M. , Favaro M. E. , Emanuel M. A. , Hess K. , Coleman J. J.
Published: July 2002

We report new experimental results on the heterostructure hot-electron diode. Improved structures, grown by metalorganic chemical vapor deposition, incorporate a single rectangular tunneling barrier of AlAs adjacent to a GaAs drift region which provides a large Γ conduction-band offset. These devices exhibit significant S-shaped negative differential resistance and dc switching at 300 K.
Infinite pleated β-sheet formed by the β-hairpin Boc-β-Phe-β-Phe-
d
-Pro-Gly-β-Phe-β-Phe-OMe
Authors: Karle Isabella , Gopi Hosahudya N. , Balaram Padmanabhan
Published: July 2002

A β-hairpin conformation and extended β-pleated sheet assembly have been characterized by single crystal x-ray diffraction for the synthetic peptide t-butoxycarbonyl—β-Phe-β-Phe-
d
-Pro-Gly-β-Phe-β-Phe-methyl ester [β-Phe: (S)-β
3
homophenylalanine]. The centrally located
d
-Pro-Gly segment nucleates a chain reversal in a type II′ β-turn conformation. Two intramolecular cross-strand hydrogen bonds stabilize the peptide fold. Intermolecular NH⋅⋅⋅O⩵C hydrogen bonds (two on each side of the hairpin) connect the hairpins into an infinitely extended β-sheet. The β-residues cause all C⩵O groups to point in the same direction, resulting in a “polar” sheet by the unidirectional alignment of NH⋅⋅⋅O⩵C hydrogen bonds. In contrast, β-sheets formed by α-residues have alternating directions for the hydrogen bonds, thus resulting in an “apolar” sheet. The crystallographic parameters for C
53
H
66
N
6
O
9
⋅CH
3
OH are: space group P2
1
,
a
= 9.854(2) Å,
b
= 10.643(2) Å,
c
= 25.296(4) Å, β = 100.39(2)°,
Z
= 2, agreement factor
R
1
= 0.065 for 3,706 data observed >4σ(
F
) and a resolution of 0.90 Å.
Cyclic peptide formation catalyzed by an antibody ligase
Authors: Smithrud David B. , Benkovic Patricia A. , Benkovic Stephen J. , Roberts Victoria , Liu Josephine , Neagu Irina , Iwama Seiji , Phillips Barton W. , Smith Amos B. , Hirschmann Ralph
Published: July 2002

Cyclic hexapeptides represent a class of compounds with important, diverse biological activities. We report herein that the antibody 16G3 catalyzes the cyclization of
d
-Trp-Gly-Pal-Pro-Gly-Phe⋅
p
-nitrophenyl ester (8a) to give
c
-(
d
-Trp-Gly-Pal-Pro-Gly-
l
-Phe) (11a). The antibody does not, however, catalyze either epimerization or hydrolysis. The resulting rate enhancement of the cyclization by 16G3 (22-fold) was sufficient to form the desired product in greater than 90% yield. In absolute rate terms, the turnover of 16G3 is estimated to be 2 min
−1
. The background rate of epimerization of 8a was reduced from 10 to 1% and hydrolysis from 50 to 4% in the presence of 16G3. As expected, the catalytic effects of 16G3 were blocked by the addition of an amount of the hapten equal to twice the antibody concentration. We also synthesized three diastereomers of 8a: the
d
-Trp
1
-
d
-Phe
6
(8b),
l
-Trp
1
-
l
-Phe
6
(8c), and
l
-Trp
1
-
d
-Phe
6
(8d) hexapeptides as well as
d
-Trp′-
l
-Trp
6
(12) and
d
-Phe′-
l
-Phe
6
(13). As expected, the rate enhancement by 16G3 was greatest for 8a, because the stereochemistry of Trp
1
and Phe
6
matches that of the corresponding residues on the hapten used to induce the biosynthesis of 16G3. A model of the variable domain of 16G3 was generated from the primary sequence using the antibody structural database to guide the model construction. The resulting model provided support for some previously proposed interpretations of the kinetic data, while providing valuable new insights for others.
Colloidal assemblies on patterned silane layers
Authors: Jonas Ulrich , del Campo Aránzazu , Krüger Christian , Glasser Gunnar , Boos Diana
Published: July 2002

The site-selective assembly of colloidal polymer particles onto laterally patterned silane layers was studied as a model system for the object assembly process at mesoscale dimensions. The structured silane monolayers on silicon oxide substrates were fabricated by a combination of liquid- and gas-phase deposition of different trialkoxysilanes with a photolithographic patterning technique. By using this method various types of surface functionalizations such as regions with amino functions next to areas of the bare silica surface or positively charged regions of a quaternary ammonium silane surrounded by a hydrophobic octadecylsilane film could be obtained. Furthermore, a triethoxysilane with a photoprotected amino group was synthesized, which allowed direct photopatterning after monolayer preparation, leading to free NH
2
groups at the irradiated regions. The different silane monolayer patterns were used to study the surface assembly behavior of carboxylated methacrylate particles by optical and scanning electron microscopy. In dependence of the assembly conditions (different surface functionalizations, pH, and drying conditions), a selective preference of the particles for a specific surface type versus others was found. Site-specific colloid adsorption could be observed also on the photosensitive silane layers after local deprotection with light. From the photosensitive silane and positively charged ammonium silane, molecularly mixed monolayers were prepared, which allowed particle adsorption and photoactivation within the same monolayer as shown by fluorescence labeling.
Shape-selective transport through rectangle-based molecular materials: Thin-film scanning electrochemical microscopy studies
Authors: Williams Mary Elizabeth , Benkstein Kurt D. , Abel Christina , Dinolfo Peter H. , Hupp Joseph T.
Published: July 2002

Microporous thin films (≈50 to 400 nm) composed of discrete, cavity-containing molecular rectangles have been prepared. The films, which contain both amorphous and microcrystalline domains, display shape-selective transport behavior. They are permeable to small molecules and to molecules that are short or narrow in at least one dimension—for example, elongated planar molecules—but are impermeable to molecules lacking a narrow dimension. However, the shape selectivity is based on transport through intramolecular rather than intermolecular cavities. By using redox-active probe molecules, rates of transport through the rectangle-based material have been extracted from electrochemical measurements. Spatially resolved measurements obtained via scanning electrochemical microscopy have permitted transport through individual microcrystals to be evaluated semiquantitatively. The measurements reveal that transport is roughly two orders of magnitude slower than observed with thin microcrystalline films of molecular squares featuring similar-sized cavities. The differences likely reflect the fact that cavities within the square-based materials, but not the rectangle-based material, align to form simple one-dimensional channels.
Trans catalysis in Tn
5
transposition
Authors: Naumann Todd A. , Reznikoff William S.
Published: July 2002

Synaptic complexes in prokaryotic transposons occur when transposase monomers bind to each of two specific end-binding sequences and then associate to bring the proteins and the two ends of the transposon together. It is within this complex of proteins and DNA that identical catalytic reactions are carried out by transposase on each of the ends of the transposon. In this study, we perform
in vitro
transposition reactions by combining the methylated inside end (IE
ME
) biased hyperactive Tn
5
transposase, Tnp sC7 version 2.0, and the outside end (OE) biased hyperactive Tn
5
transposase, Tnp EK/LP, with plasmid DNA containing a transposon defined by one IE
ME
and one OE. These two proteins cooperate to facilitate double end cleavage of the transposon from the plasmid and conversion into transposition products via strand transfer. When one of the hyperactive Tnps is replaced with a catalytically inactive version containing the mutation EA326 (DDE mutant), the predominant reaction product is a linearized plasmid resulting from single end cleavage. Restriction analysis of these linear products reveals that cleavage is occurring on the end distal to that which is bound by the transposase with an intact active site or
in trans
. Similar
in vitro
experiments performed with precut transposons and a supercoiled target plasmid demonstrated that the strand transfer reaction is also facilitated by a trans active DDE motif.
U1 small nuclear RNA chimeric ribozymes with substrate specificity for the Rev pre-mRNA of human immunodeficiency virus.
Authors: Michienzi A , Prislei S , Bozzoni I
Published: July 2002

The in vivo effectiveness of ribozymes strongly depends on the correct choice of the vector molecule. High levels of expression, stability, active conformation, and correct cellular localization are the most important features for a ribozyme vector. We have exploited the utilization of the U1 small nuclear RNA (snRNA) as a vector for specifically targeting a ribozyme into the nucleus. The Rev pre-mRNA of human immunodeficiency virus type 1 was chosen as target for testing the activity of the Ul-ribozyme. The catalytic core of the hammerhead motif, plus the recognition sequences, substituted the stem-loop III of the U1 snRNA. The resulting construct displays efficient cleavage activity in vitro. In addition, in the in vivo system of Xenopus laevis oocytes, the Ul-chimeric ribozyme accumulates in large amounts in the nucleus and produces a considerable reduction of Rev pre-mRNA levels. The Rev-specific ribozyme was also inserted in a derivative of the Ul snRNA mutated in the region of pairing with the 5' splice site, such as to match it with the suboptimal splice junction of the Rev precursor. This construct shows more efficient reduction of Rev pre-mRNA in vivo than the wild-type U1 vector.
The differential adhesion forces of anterior cruciate and medial collateral ligament fibroblasts: effects of tropomodulin, talin, vinculin, and alpha-actinin.
Authors: Sung K L , Yang L , Whittemore D E , Shi Y , Jin G , Hsieh A H , Akeson W H , Sung L A
Published: July 2002

We have determined the effects of tropomodulin (Tmod), talin, vinculin, and alpha-actinin on ligament fibroblast adhesion. The anterior cruciate ligament (ACL), which lacks a functional healing response, and the medial collateral ligament (MCL), a functionally healing ligament, were selected for this study. The micropipette aspiration technique was used to determine the forces needed to separate ACL and MCL cells from a fibronectin-coated surface. Delivery of exogenous tropomodulin, an actin-filament capping protein, into MCL fibroblasts significantly increased adhesion, whereas its monoclonal antibody (mAb) significantly decreased cell adhesiveness. However, for ACL fibroblasts, Tmod significantly reduced adhesion, whereas its mAb had no effect. mAbs to talin, vinculin, and alpha-actinin significantly decreased the adhesion of both ACL and MCL cells with increasing concentrations of antibody, and also reduced stress fiber formation and cell spreading rate as revealed by immunofluorescence microscopy. Disruption of actin filament and microtubule assembly with cytochalasin D and colchicine, respectively, also significantly reduced adhesion in ACL and MCL cells. In conclusion, both ACL and MCL fibroblast adhesion depends on cytoskeletal assembly; however, this dependence differs between ACL and MCL fibroblasts in many ways, especially in the role of Tmod. These results add yet another possible factor in explaining the clinical differences in healing between the ACL and the MCL.
Room-temperature single-electron junction.
Authors: Facci P , Erokhin V , Carrara S , Nicolini C
Published: July 2002

The design, realization, and test performances of an electronic junction based on single-electron phenomena that works in the air at room temperature are hereby reported. The element consists of an electrochemically etched sharp tungsten stylus over whose tip a nanometer-size crystal was synthesized. Langmuir-Blodgett films of cadmium arachidate were transferred onto the stylus and exposed to a H2S atmosphere to yield CdS nanocrystals (30-50 angstrom in diameter) imbedded into an organic matrix. The stylus, biased with respect to a flat electrode, was brought to the tunnel distance from the film and a constant gap value was maintained by a piezo-electric actuator driven by a feedback circuit fed by the tunneling current. With this set-up, it is possible to measure the behavior of the current flowing through the quantum dot when a bias voltage is applied. Voltage-current characteristics measured in the system displayed single-electron trends such as a Coulomb blockade and Coulomb staircase and revealed capacitance values as small as 10(-19) F.
Expression of αv and β3 integrin chains on murine lymphocytes
Authors: Gerber David J. , Pereira Pablo , Huang Shu Ying , Pelletier Claire , Tonegawa Susumu
Published: July 2002

The vitronectin receptor is a member of the integrin family of adhesion protein receptors and binds a broad spectrum of ligands, including fibronectin and fibrinogen in addition to vitronectin. We have generated four mAbs that recognize the murine αvβ3 vitronectin receptor. Biochemical and expression analyses showed that two of the mAbs are specific for the αv chain, and two are specific for the β3 chain. The mAbs are effective blocking reagents and inhibited cell adhesion to vitronectin, fibrinogen, and fibronectin. Staining analysis revealed expression of αv and β3 on certain populations of murine thymocytes, splenocytes, and bone marrow cells. The expression of αv and β3 appeared to be modulated at specific stages of thymocyte development, suggesting a possible function for the αvβ3 vitronectin receptor in T cell development.
Reduction in receptors for bombesin and epidermal growth factor in xenografts of human small-cell lung cancer after treatment with bombesin antagonist RC-3095
Authors: Halmos Gabor , Schally Andrew V.
Published: July 2002

Antagonists of bombesin/gastrin-releasing peptide (BN/GRP) have been developed to inhibit the stimulatory effects of BN/GRP on the mitogenesis of tumor cells such as human small-cell lung carcinoma (SCLC). The mode of action of these antagonists is not completely understood. In this study, we evaluated the effect of BN/GRP antagonist RC-3095 on receptors for BN/GRP and epidermal growth factor (EGF) in H-128 human SCLC line xenografted into nude mice. Treatment with RC-3095, administered s.c. at a dose of 20 μg/day per animal for 4 weeks caused a 70% reduction in tumor volume and weight. Membrane receptors for BN/GRP and EGF were characterized in untreated and treated animals. In the control group, [
125
I-Tyr
4
]BN was bound to a single class of specific, high affinity binding sites with a dissociation constant (
K
d
) = 6.55 ± 0.93 nM and maximal binding capacity (
B
max
) = 512.8 ± 34.8 fmol/mg membrane protein. Therapy with RC-3095 decreased the concentration of BN/GRP receptors on H-128 SCLC tumor membranes. Specific, high affinity binding sites for EGF with
K
d
= 1.78 ± 0.26 nM and
B
max
= 216.8 ± 19.6 fmol/mg membrane protein were also found on the untreated H-128 SCLC tumors. Treatment with RC-3095 significantly decreased
B
max
of receptors for EGF. Our results indicate that the suppression of growth of H-128 SCLC by BN antagonist RC-3095 is accompanied by a decrease in the number of receptors for both BN/GRP and EGF. These observations are in agreement with the results obtained in other experimental cancers. The findings on antagonist RC-3095 reinforce the view that both BN/GRP and EGF receptors participate in a cascade of events involved in the growth of SCLC and other cancers. Although the complete mechanisms of action of antagonist RC-3095 remain to be elucidated, the antitumor effect could be the result of the fall in the EGF receptor number, which might lead to a decrease in EGF receptor autophosphorylation.
A model for the structure of the P domains in the subtilisin-like prohormone convertases
Authors: Lipkind Gregory M. , Zhou An , Steiner Donald F.
Published: July 2002

The proprotein convertases are a family of at least seven calcium-dependent endoproteases that process a wide variety of precursor proteins in the secretory pathway. All members of this family possess an N-terminal proregion, a subtilisin-like catalytic module, and an additional downstream well-conserved region of ≈150 amino acid residues, the P domain, which is not found in any other subtilase. The pro and catalytic domains cannot be expressed in the absence of the P domains; their thermodynamic instability may be attributable to the presence of large numbers of negatively charged Glu and Asp side chains in the substrate binding region for recognition of multibasic residue cleavage sites. Based on secondary structure predictions, we here propose that the P domains consist of 8-stranded β-barrels with well-organized inner hydrophobic cores, and therefore are independently folded components of the proprotein convertases. We hypothesize further that the P domains are integrated through strong hydrophobic interactions with the catalytic domains, conferring structural stability and regulating the properties and activity of the convertases. A molecular model of these interdomain interactions is proposed in this report.
Male-specific transcription initiation of theC4-Slpgene in mouse liver follows activation of STAT5
Authors: Varin-Blank N. , Dondi E. , Tosi M. , Hernandez C. , Boucontet L. , Gotoh H. , Shiroishi T. , Moriwaki K. , Meo T.
Published: July 2002

The mouse genes encoding the constitutively expressed complement component C4 and its closely related isoform C4-Slp (sex-limited protein), which is expressed only in male animals of several strains, provide a unique model to study sequence elements and trans-acting factors responsible for androgen responsiveness. Our previous studies have shown that hormonal induction ofC4-Slpis mediated by a sex-specific pattern of growth hormone secretion. Promoter analysesin vitrohave led to contradictory conclusions concerning the significance ofC4-Slp-specific sequences in the 5′ flanking region. Mutant mice carrying theH-2aw18haplotype, which is characterized by a large deletion in theSregion covering theC4and21-OHase Agenes, permit the directin vivoanalysis ofC4-Slptranscription, unhindered by the presence ofC4. Run-on analysis of transcription in liver nuclei of males and females of this strain demonstrated a 100-fold higher transcriptional activity in males, essentially determined at the transcription initiation level. The androgen dependence of transcription initiation was confirmed by run-on analysis of testosterone-treated females, where transcriptional activity started after 6 days of androgen treatment and reached male levels after 20 days. Conversely, the growth hormone-regulated activity of transcription factor STAT5 was already detected in liver nuclei after 48 hr of androgen treatment. Furthermore, we demonstrate that activated STAT5 recognizesin vitrotwo upstream γ interferon-activated sequence (GAS) elements of theC4-Slpgene, centered at positions −1969 and −1831. We postulate that binding of STAT5 to these C4-Slp-specific GAS elements plays a crucial role in the chromatin remodelings that lead to transcriptional competence of theC4-Slpgene in the liver.
Induction of an apoptotic program in cell-free extracts by 2-chloro-2′-deoxyadenosine 5′-triphosphate and cytochrome c
Authors: Leoni Lorenzo M. , Chao Qi , Cottam Howard B. , Genini Davide , Rosenbach Michael , Carrera Carlos J. , Budihardjo Imawati , Wang Xiaodong , Carson Dennis A.
Published: July 2002

Adenine deoxynucleosides, such as 2-chloro-2′-deoxyadenosine (2CdA) induce apoptosis in quiescent lymphocytes, and are thus useful drugs for the treatment of indolent lymphoproliferative diseases. However, it has remained puzzling why deoxyadenosine and its analogs are toxic to a cell that is not undergoing replicative DNA synthesis. The present experiments demonstrate that the 5′-triphosphate metabolite of 2CdA (2CdA-5′-triphosphate), similar to dATP, can cooperate with cytochromecand Apaf-1 to activate caspase-3 in a cell free system. Chronic lymphocytic leukemia cells and normal peripheral blood lymphocytes expressed both caspase-3 and apoptotic protease activating factor 1. Incubation of the lymphocytes with 2CdA induced caspase-3 activation prior to DNA degradation and cell death. Stimulation of the caspase proteolytic cascade by 2CdA-5′-triphosphate, in the context of DNA strand break formation, may provide an explanation for the potent cytotoxic effects of 2CdA toward nondividing lymphocytes.
Mitogen-activated protein kinase and neural specification inXenopus
Authors: Uzgare Aarti R. , Uzman J. Akif , El-Hodiri Heithem M. , Sater Amy K.
Published: July 2002

We have investigated the activity and function of mitogen-activated protein kinase (MAPK) during neural specification inXenopus. Ectodermal MAPK activity increased between late blastula and midgastrula stages. At midgastrula, MAPK activity in both newly induced neural ectoderm and ectoderm overexpressing the anterior neural inducer noggin was 5-fold higher than in uninduced ectoderm. Overexpression of MAPK phosphatase-1 (MKP-1) in ectoderm inhibited MAPK activity and prevented neurectoderm-specific gene expression when the ectoderm was recombined with dorsal mesoderm or treated with fibroblast growth factor (FGF). Neurectoderm-specific gene expression was observed, however, in ectoderm overexpressing both noggin and MKP-1. To evaluate the role of MAPK in posterior regionalization, ectodermal isolates were treated with increasing concentrations of FGF and assayed for MAPK activity and neurectoderm-specific gene expression. Although induction of posterior neural ectoderm by FGF was accompanied by an elevation of MAPK activity, relative MAPK activity associated with posterior neural fate was no higher than that of ectoderm specified to adopt an anterior neural fate. Thus, increasingly posterior neural fates are not correlated with quantitative increases in MAPK activity. Because MAPK has been shown to down-regulate Smad1, MAPK may disrupt bone morphogenetic protein 4 (BMP-4) signaling during neural specification. Our results suggest that MAPK plays an essential role in the establishment of neural fatein vivo.
Isolation and characterization of iron-independent positive dominant mutants of the diphtheria toxin repressor DtxR
Authors: Sun Li , vanderSpek Johanna , Murphy John R.
Published: July 2002

It is well known that the functional activity of the diphtheria toxin repressor DtxR is controlled by iron, which serves as an essential cofactor necessary for activation of target DNA binding by this regulatory element. In this communication, we describe the isolation and characterization of a unique series of DtxR mutants that are constitutively active and repress the expression of β-galactosidase from a diphtheria
tox
promoter/operator–
lac
Z transcriptional fusion, even in the absence of iron. These self-activating mutants of DtxR (SAD) were isolated through the use of a positive selection system for the cloning of functional d
tx
R alleles and target DNA operator sites. Of the four independently isolated SAD mutants that were characterized, two (SAD2 and SAD11) were found to carry a single missense mutation (E175K) in their respective C-terminal SH3-like domains. In contrast, the mutant allele encoding SAD3 was found to carry a total of six missense mutations distributed throughout the N- and C-terminal domains of the repressor. Partial diploid analysis of strains carrying both native
dtx
R and alleles encoding either SAD2 or SAD3 demonstrate that these iron-independent mutants possess a positive dominant phenotype in the regulation of β-galactosidase expression from a diphtheria
tox
promoter/operator–
lac
Z transcriptional fusion.
Dendritic cell maturation and antigen presentation in the absence of invariant chain
Authors: Rovere Patrizia , Zimmermann Valérie S. , Forquet Frédérique , Demandolx Denis , Trucy Jeannine , Ricciardi-Castagnoli Paola , Davoust Jean
Published: July 2002

In immature dendritic cells (DCs), major histocompatibility complex class II molecules accumulate in peptide-loading compartments and, during DC maturation, are exported to the cell surface in response to inflammatory stimuli. Moreover, it has recently been proposed that DCs have specific mechanisms of antigen uptake and delivery into major histocompatibility complex class II-loading compartments. B cells bearing a genetically disrupted invariant chain gene (Ii −/−) show alterations in the transport and function of class II molecules. We herein report that DCs derived from Ii −/− H2kbut not Ii −/− H2bmice undergo normal maturation in response to tumor necrosis factor α and show a high degree of class II surface expression. Class II molecules are accumulated in cathepsin D- and H2-M-positive compartments in immature Ii −/− DC and, during DC maturation, are exported to the cell membrane as compact dimers. Ii −/− DCs present putative Ii-dependent hen egg lysozyme-derived epitopes to T cells. These data support the existence of Ii-independent molecular requirements for class II transport and peptide loading in DCs.
Costimulatory signals are required for induction of transcription factor Nur77 during negative selection of CD4+CD8+thymocytes
Authors: Amsen Derk , Calvo Conchi Revilla , Osborne Barbara A. , Kruisbeek Ada M.
Published: July 2002

A major question in end-stage T cell development is how T cell receptor(TCR) ligation on immature CD4+CD8+double positive thymocytes is translated into either survival (positive selection) or apoptotic (negative selection) signals. Because different types of antigen-presenting cells (APCs) induce positive or negative selection in the thymus and express different costimulatory molecules, involvement of such costimulatory molecules in determining cell fate of DP thymocytes is considered here. If TCR-generated signals are modulated by APCs, this should be reflected in the activation of distinct biochemical pathways. We here demonstrate that costimulatory signals involved in negative selection also are required for induction of protein expression of Nur77 and its family members. These transcription factors are critically involved in negative but not positive selection. In contrast, the signals that costimulate negative selection are not required for induction of several molecular events associated with positive selection. These include activation of the immediate early gene Egr-1, the mitogen-activated protein kinase ERK2, and surface expression of the CD69 marker. Thus, costimulation for negative selection selectively provides signals for activation of apoptotic mediators. These data provide molecular insights into how TCR-engagement by ligands on different thymic APCs can determine cell fate.
Book Reviews
Authors: MICHAEL MICHAEL
Published: July 2002

Book reviewed in this article:

Growing Up Tobacco Free: Preventing Nicotine Addiction in Children and Youths BARBARA S. LYNCH & RICHARD J. BONNIE (Eds)

Nicotine Addiction: Principles and Management C. TRACY ORLEANS & JOHN SLADE (Eds)

Alcohol Treatment: A Study of Therapists and Clients J. KEENE

Drinking Careers: A Twenty‐Five‐Year Study of Three Navajo Populations STEPHEN J. KUNITZ & JERROLD E. LEVY

Drug and Alcohol Abuse MARC A. SCHUCKIT

Preventing AIDS: Theories and Methods of Behavioral Interventions RALPH J. DICLEMENTE & JOHN L. PETERSON
Anxiety and pupil reactivity in cocaine dependent subjects endorsing cocaine‐induced paranoia: preliminary report
Authors: ROSSE RICHARD B. , ALIM TANYA N. , JOHRI SURENDRA K. , HESS ANEMARIE L. , DEUTSCH STEPHEN I.
Published: July 2002

There has been the clinical impression that people with higher levels of anxiety and central arousal are more prone to develop cocaine‐induced paranoia (CIP), but this notion has not been formally studied. In the current study, we examined the differences between 28 CIP‐endorsing and 16 CIP‐denying chronic cocaine users in their levels of state and trait anxiety as measured by the Spielberger State‐Tail Anxiety Inventory. We also studied levels of central arousal and reactivity using pupil size measures both during exposure to neutral, abstract, non‐drug cues, and after exposure to a cocaine cue. Levels of trait (but not state) anxiety were significantly higher in the CIP group than in the non‐CIP group. Moreover, while there were no significant pupil size differences or changes between the two groups while viewing neutral, abstract video images, the CIP group had significantly greater pupillary dilation in response to a video image of crack cocaine than did the non‐CIP group. These significant differences remained even after covarying for anxiety scores. The study findings seem relevant to studies of autonomic reactivity in response to drug cues in cocaine‐dependent patients; such studies might remain attentive to potential cue reactivity differences between patients endorsing and those denying CIP. Finally, this is the first study showing higher trait anxiety in patients with CIP.
Encounters with aggressive conspecifics enhance the locomotor‐activating effects of cocaine in the rat
Authors: MARROW LYNNE P. , OVERTON PAUL G. , BRAIN PAUL F. , CLARK DAVID
Published: July 2002

Evidence suggests that stress enhances the behavioural actions of cocaine in the rat. Paradoxically, however, encounters with aggressive conspecifics lead to a pattern of cocaine self‐administration indicative of a reduced functional impact of the drug. Hence, we examined the effects of aggressive encounters on another behavioural measure‐locomotor activity. Encounters between Lister Hooded rats and rats of the aggressive Tryon Maze Dull strain significantly enhanced the locomotor‐activating effects of cocaine (20 mg/kg) in the Lister Hooded rats. The results suggest that the discrepant findings derived from self‐administration studies are a property of the paradigm rather than a property of the stressor.
Electrocardiographic abnormalities during recovery from ultra‐short opiate detoxification
Authors: ALLHOFF THOMAS , RENZING‐KÖHLER KATRIN , KIENBAUM PETER , SACK STEFAN , SCHERBAUM NORBERT
Published: July 2002

The aim of this study was to detect electrocardiographic abnormalities during recovery from ultra‐short opiate detoxification, using a retrospective study design conducted at a university hospital. Twenty‐two consecutive patients (mean±SD, age 30.0±6.3 years) receiving daily oral methadone underwent ultrashort opiate detoxification under general anaesthesia. In the post‐anaesthetic stages they received oral clonidine and naltrexone, and in some cases trimipramine was dispensed. Heart rate, rate‐corrected QT interval (msec) and repolarization abnormalities of 12‐lead electrocardiographic recordings before and after detoxification were examined. The serum electrolyte concentrations (mmol/l) including Na+, K+ and Ca2+ were assessed. Eightyone ECGs were evaluated in total. Compared to the initial values, heart rate was significantly lowered in the first two tracings after detoxification (median values 60.0/min. vs. 52,5/min; p=0.0006). The lowest heart rate measured after detoxification was 44/min. The cQT interval was significantly lengthened (median value 420 msec vs. 453 msec after detoxification). In 16 tracings (20%) taken from 10 patients (45%) cQT rose above 460 msec and in two tracings (2%) it topped 500 msec. Modest hypokalaemia (2.9–3.5 mmol/l) was linked to cQT prolongation (460 msec) in 10 ECG tracings. Spearman's correlation coefficient indicated that prolonged cQT intervals correlated with decreased potassium values. Twelve tracings (15%) taken from 10 patients (45%) after detoxification showed T‐wave inversion and in two cases sinus rhythm was turned into a rhythm arising from the atrioventricular node. Serum potassium was significantly lowered (median values 4.3 v.s 3.8 mmol/l, p=0.0001). The Ca2+ concentration fell significantly (2.4 vs. 2.2 mmol/l, p=0.0001) but not below the normal range. It was concluded that ultra‐short opiate detoxification carries the risk of QTprolongation and bradycardia. These side effects are reversible and can be explained by hypokalaemia and clonidine medication, the effects of which might reinforce each other. To avoid arrhythmic complications, ECG tracings should be carried out regularly during recovery, i.e. at least daily, for a span of 3 days after discharge from the intensive care unit.
Regulation of DNA Replication During the Cell Cycle: Roles of Cdc7 Kinase and Coupling of Replication, Recombination, and Repair in Response to Replication Fork Arrest
Authors: Masai Hisao , Arai Ken‐ichi
Published: July 2002

DNA replication is central to cell growth, development, and generation of tissues and organs. Recent advances in understanding replication machinery have revealed striking conservation of components involved in the processes of DNA replication, from yeasts to human. The conservation extends even to bacteria for some basic components of replication apparatus. Eukaryotic DNA replication is regulated at various stages to ensure strict regulation during cell cycle. We have identified a novel mammalian kinase, Cdc7‐ASK (Activator of S phase Kinase), that plays a key role at the entry into S phase as a molecular switch for DNA replication. This kinase is specifically activated during S phase and triggers the firing of DNA replication by phosphorylating an essential DNA helicase component of the replication complex. Environmental stresses such as DNA damages or depletion of essential nutrients for DNA synthesis lead to unscheduled arrest of DNA replication forks. In bacteria, this leads to induction of altered modes of DNA replication, which may repair DNA damages, facilitate reassembly of replication machinery at the stalled replication fork, or do both. In eukaryotes, blocking replication forks usually induces both checkpoint responses, which prevent premature progression of cell cycle events before precise completion of the preceding cell cycle stage, and the recombinational repair system for the lesions. Possible common bases in recognition of stalled replication forks in bacteria and eukaryotes will be discussed. Furthermore, we will discuss the potential of replication and checkpoint proteins as targets of anticancer agents as well as possible novel technology for stem cell amplification through manipulation of DNA replication.