New Light on Molecule-Nanotube Hybrids

Optoelectronics benefits from outstanding new nanomaterials that provide emission and detection in the visible and near-infrared range, photoswitches, two level systems for single photon emission, etc. Among these, carbon nanotubes are envisioned as game changers despite difficult handling and control over chirality burdening their use. However, recent breakthroughs on hybrid carbon nanotubes have established nanotubes as pioneers for a new family of building blocks for optics and quantum optics. Functionalization of carbon nanotubes with molecules or polymers not only preserves the nanotube properties from the environment, but also promotes new performance abilities to the resulting hybrids. Photoluminescence and Raman signals are enhanced in the hybrids, which questions the nature of the electronic coupling between nanotube and molecules. Furthermore, coupling to optical cavities dramatically enhances single photon emission, which operates up to room temperature. This new light on nanotube hybrids shows their potential to push optoelectronics a step forward.

Coherence and Density Dynamics of Excitons in a Single-Layer MoS2 Reaching the Homogeneous Limit

We measure the coherent nonlinear response of excitons in a single layer of molybdenum disulfide embedded in hexagonal boron nitride, forming a h-BN/MoS₂/ h-BN heterostructure. Using four-wave mixing microscopy and imaging, we correlate the exciton inhomogeneous broadening with the homogeneous one and population lifetime. We find that the exciton dynamics is governed by microscopic disorder on top of the ideal crystal properties. Analyzing the exciton ultrafast density dynamics using amplitude and phase of the response, we investigate the relaxation pathways of the resonantly driven exciton population. The surface protection via encapsulation provides stable monolayer samples with low disorder, avoiding surface contaminations and the resulting exciton broadening and modifications of the dynamics. We identify areas localized to a few microns where the optical response is totally dominated by homogeneous broadening. Across the sample of tens of micrometers, weak inhomogeneous broadening and strain effects are observed, attributed to the remaining interaction with the h-BN and imperfections in the encapsulation process.

Weakly Trapped, Charged, and Free Excitons in Single-Layer MoS2 in the Presence of Defects, Strain, and Charged Impurities

Few- and single-layer MoS₂ host substantial densities of defects. They are thought to influence the doping level, the crystal structure, and the binding of electron-hole pairs. We disentangle the concomitant spectroscopic expression of all three effects and identify to what extent they are intrinsic to the material or extrinsic to it, i.e., related to its local environment. We do so by using different sources of MoS₂-a natural one and one prepared at high pressure and high temperature-and different substrates bringing varying amounts of charged impurities and by separating the contributions of internal strain and doping in Raman spectra. Photoluminescence unveils various optically active excitonic complexes. We discover a defect-bound state having a low binding energy of 20 meV that does not appear sensitive to strain and doping, unlike charged excitons. Conversely, the defect does not significantly dope or strain MoS₂. Scanning tunneling microscopy and density functional theory simulations point to substitutional atoms, presumably individual nitrogen atoms at the sulfur site. Our work shows the way to a systematic understanding of the effect of external and internal fields on the optical properties of two-dimensional materials.

Light Control of Charge Transfer and Excitonic Transitions in a Carbon Nanotube/Porphyrin Hybrid

Carbon nanotube-chromophore hybrids are promising building blocks in order to obtain a controlled electro-optical transduction effect at the single nano-object level. In this work, a strong spectral selectivity of the electronic and the phononic response of a chromophore-coated single nanotube transistor is observed for which standard photogating cannot account. This paper investigates how light irradiation strongly modifies the coupling between molecules and nanotube within the hybrid by means of combined Raman diffusion and electron transport measurements. Moreover, a nonconventional Raman enhancement effect is observed when light irradiation is on the absorption range of the grafted molecule. Finally, this paper shows how the dynamics of single electron tunneling in the device at low temperature is strongly modified by molecular photoexcitation. Both effects will be discussed in terms of photoinduced excitons coupled to electronic levels.

Biaxial Strain Transfer in Supported Graphene

Understanding the mechanism and limits of strain transfer between supported 2D systems and their substrate is a most needed step toward the development of strain engineering at the nanoscale. This includes applications in straintronics, nanoelectromechanical devices, or new nanocomposites. Here, we have studied the limits of biaxial compressive strain transfer among SiO₂, diamond, and sapphire substrates and graphene. Using high pressure-which allows maximizing the adhesion between graphene and the substrate on which it is deposited-we show that the relevant parameter governing the graphene mechanical response is not the applied pressure but rather the strain that is transmitted from the substrate. Under these experimental conditions, we also show the existence of a critical biaxial stress beyond which strain transfer become partial and introduce a parameter, α, to characterize strain transfer efficiency. The critical stress and α appear to be dependent on the nature of the substrate. Under ideal biaxial strain transfer conditions, the phonon Raman G-band dependence with strain appears to be linear with a slope of -60 ± 3 cm^-1/% down to biaxial strains of -0.9%. This evolution appears to be general for both biaxial compression and tension for different experimental setups, at least in the biaxial strain range -0.9% < ε < 1.8%, thus providing a criterion to validate total biaxial strain transfer hypotheses. These results invite us to cast a new look at mechanical strain experiments on deposited graphene as well as to other 2D layered materials.

Strain superlattices and macroscale suspension of graphene induced by corrugated substrates

We investigate the organized formation of strain, ripples, and suspended features in macroscopic graphene sheets transferred onto corrugated substrates made of an ordered array of silica pillars with variable geometries. Depending on the pitch and sharpness of the corrugated array, graphene can conformally coat the surface, partially collapse, or lie fully suspended between pillars in a fakir-like fashion over tens of micrometers. With increasing pillar density, ripples in collapsed films display a transition from random oriented pleats emerging from pillars to organized domains of parallel ripples linking pillars, eventually leading to suspended tent-like features. Spatially resolved Raman spectroscopy, atomic force microscopy, and electronic microscopy reveal uniaxial strain domains in the transferred graphene, which are induced and controlled by the geometry. We propose a simple theoretical model to explain the structural transition between fully suspended and collapsed graphene. For the arrays of high density pillars, graphene membranes stay suspended over macroscopic distances with minimal interaction with the pillars' apexes. It offers a platform to tailor stress in graphene layers and opens perspectives for electron transport and nanomechanical applications.

Functional hybrid systems based on large-area high-quality graphene

The properties of sp² carbon allotropes can be tuned and enriched by their interaction with other materials. The large interface to the outside world in these forms of carbon is ideally suited for combining in an optimal manner several functionalities thanks to this interaction. A wide range of novel materials holding strong promise in energy, optoelectronics, microelectronics, mechanics, or medical applications have been designed accordingly. Graphene, the last representative of this family of sp² carbon materials, has already yielded a wealth of hybrid systems. A new class of these hybrids is emerging, which allows researchers to exploit the properties of truly single-layer graphene. These systems rely on high-quality graphene. In this Account, we describe our recent efforts to develop hybrid systems through various approaches and with various scopes. Depending on the interaction between graphene and molecules, metal clusters, layers, and substrates, either graphene may essentially preserve the electronic properties that make it a unique platform for electronic transport, or new organization and properties in the materials may arise due to the graphene contact at the expense of deep modification of graphene's properties. We prepare our graphene samples by both mechanical exfoliation of graphite and chemical vapor deposition on metals. We use this to study graphene in contact with various species, which either decorate graphene or are intercalated between it and its substrate. We first address the electronic and magnetic properties in systems where graphene is in epitaxy with a metal and discuss the potential to manipulate the properties of both materials, highlighting graphene's role as a protective capping layer in magnetic functional systems. We then present graphene/metal dot hybrids, which can utilize the two-dimensional gas properties of Dirac fermions in graphene. These hybrids allow one to tune the coupling between clusters hosting electronically ordered states such as superconductivity and explore quantum phase transitions controlled by electrostatic back gates. We finally discuss the optical properties of hybrids in which graphene is decorated with optically active molecules. Depending on how close these molecules are to the graphene's electromechanical systems, the interaction of the system with light can be changed. Fields such as spintronics and catalysis could benefit from high-quality graphene based hybrid systems, which have not been fully explored.

The tracking control system of the VLT Survey Telescope

The VLT survey telescope is the latest telescope installed at European Southern Observatory's Paranal observatory that is considered one of the best sites for optical astronomy for the excellent seeing conditions. The exceptional quality of the site imposes tight requirements for the telescope tracking system that shall perform very well to fully exploit the extreme sharpness of the Chilean sky. We describe the specific solutions adopted for pointing, servo and guiding systems and the results obtained during the commissioning of the telescope. The hardware implementation relies on industry components and the control solutions privilege both the performance and the future maintainability of the system.

A local optical probe for measuring motion and stress in a nanoelectromechanical system

Nanoelectromechanical systems can be operated as ultrasensitive mass sensors and ultrahigh-frequency resonators, and can also be used to explore fundamental physical phenomena such as nonlinear damping and quantum effects in macroscopic objects. Various dissipation mechanisms are known to limit the mechanical quality factors of nanoelectromechanical systems and to induce aging due to material degradation, so there is a need for methods that can probe the motion of these systems, and the stresses within them, at the nanoscale. Here, we report a non-invasive local optical probe for the quantitative measurement of motion and stress within a nanoelectromechanical system, based on Fizeau interferometry and Raman spectroscopy. The system consists of a multilayer graphene resonator that is clamped to a gold film on an oxidized silicon surface. The resonator and the surface both act as mirrors and therefore define an optical cavity. Fizeau interferometry provides a calibrated measurement of the motion of the resonator, while Raman spectroscopy can probe the strain within the system and allows a purely spectral detection of mechanical resonance at the nanoscale.

Magneto-Coulomb effect in carbon nanotube quantum dots filled with magnetic nanoparticles

Electrical transport measurements of carbon nanotubes filled with magnetic iron nanoparticles are reported. Low-temperature (40 mK) magnetoresistance measurements showed conductance hysteresis with sharp jumps at the switching fields of the nanoparticles. Depending on the gate voltage, positive or negative hysteresis was observed. The results are explained in terms of a magneto-Coulomb effect: The spin flip of the iron island at a nonzero magnetic field causes a shift of the chemical potential induced by the change of Zeeman energy; i.e., an effective charge variation is detected by the nanotube quantum dot.

Surface-enhanced Raman signal for terbium single-molecule magnets grafted on graphene

We report the preparation and characterization of monolayer graphene decorated with functionalized single-molecule magnets (SMMs). The grafting ligands provide a homogeneous and selective deposition on graphene. The grafting is characterized by combined Raman microspectroscopy, atomic force microscopy (AFM), and electron transport measurements. We observe a surface-enhanced Raman signal that allowed us to study the grafting down to the limit of a few isolated molecules. The weak interaction through charge transfer is in agreement with ab initio DFT calculations. Our results indicate that both molecules and graphene are essentially intact and the interaction is driven by van der Waals forces.

Electroluminescence from single-wall carbon nanotube network transistors

The electroluminescence (EL) properties from single-wall carbon nanotube network field-effect transistors (NNFETs) and small bundle carbon nanotube field effect transistors (CNFETs) are studied using spectroscopy and imaging in the near-infrared (NIR). At room temperature, NNFETs produce broad (approximately 180 meV) and structured NIR spectra, while they are narrower (approximately 80 meV) for CNFETs. EL emission from NNFETs is located in the vicinity of the minority carrier injecting contact (drain) and the spectrum of the emission is red shifted with respect to the corresponding absorption spectrum. A phenomenological model based on a Fermi-Dirac distribution of carriers in the nanotube network reproduces the spectral features observed. This work supports bipolar (electron-hole) current recombination as the main mechanism of emission and highlights the drastic influence of carrier distribution on the optoelectronic properties of carbon nanotube films.

Confocal imaging of glutathione redox potential in living plant cells

Reduction-oxidation-sensitive green fluorescent protein (roGFP1 and roGFP2) were expressed in different sub-cellular compartments of Arabidopsis and tobacco leaves to empirically determine their performance as ratiometric redox sensors for confocal imaging in planta. A lower redox-dependent change in fluorescence in combination with reduced excitation efficiency at 488 nm resulted in a significantly lower dynamic range of roGFP1 than for roGFP2. Nevertheless, when targeted to the cytosol and mitochondria of Arabidopsis leaves both roGFPs consistently indicated redox potentials of about -320 mV in the cytosol and -360 mV in the mitochondria after pH correction for the more alkaline matrix pH. Ratio measurements were consistent throughout the epidermal cell layer, but results might be attenuated deeper within the leaf tissue. Specific interaction of both roGFPs with glutaredoxin in vitro strongly suggests that in situ both variants preferentially act as sensors for the glutathione redox potential. roGFP2 targeted to plastids and peroxisomes in epidermal cells of tobacco leaves was slightly less reduced than in other plasmatic compartments, but still indicated a highly reduced glutathione pool. The only oxidizing compartment was the lumen of the endoplasmic reticulum, in which roGFP2 was almost completely oxidized. In all compartments tested, roGFP2 reversibly responded to perfusion with H(2)O(2) and DTT, further emphasizing that roGFP2 is a reliable probe for dynamic redox imaging in planta. Reliability of roGFP1 measurements might be obscured though in extended time courses as it was observed that intense irradiation of roGFP1 at 405 nm can lead to progressive photoisomerization and thus a redox-independent change of fluorescence excitation ratios.

Exciton formation and annihilation during 1D impact excitation of carbon nanotubes

Near-infrared electroluminescence was recorded from unipolar single-wall carbon nanotube field-effect transistors at high drain-source voltages. High resolution spectra reveal resonant light emission originating from the radiative relaxation of excitons rather than heat dissipation. The electroluminescence is induced by only one carrier type and ascribed to 1D impact excitation. An emission quenching is also observed at high field and attributed to an exciton-exciton annihilation process and free carrier generation. The excitons' binding energy in the order of 270 meV for 1.4 nm SWNTs is inferred from the spectral features.

Self-assembly of carbon-nanotube-based single-electron memories

We demonstrate the wafer-scale integration of single-electron memories based on carbon nanotube field-effect transistors (CNFETs) using a process based entirely on self assembly. First, a "dry" self-assembly step based on chemical vapor deposition (CVD) allows the growth and connection of CNFETs. Next, a "wet" self-assembly step is used to attach a single 30-nm-diameter gold bead in the nanotube vicinity via chemical functionalization. The bead is used as the memory storage node while the CNFET operating in the subthreshold regime acts as an electrometer exhibiting exponential gain. Below 60 K, the transfer characteristics of gold-CNFETs show highly reproducible hysteretic steps. Evaluation of the capacitance confirms that these current steps originate from the controlled storage of single electrons with a retention time that exceeds 550 s at 4 K.

Raman Spectroscopy of Free-Standing Individual Semiconducting Single-Wall Carbon Nanotubes

The radial breathing modes and tangential modes have been systematically measured on a large number of individual semiconducting single-wall carbon nanotubes (thin bundles) suspended between plots (free-standing single-wall carbon nanotubes). The strong intensity of the Raman spectra ensures the precision of the experimentally determined line shapes and frequencies of these modes. The diameter dependence of the frequencies of the tangential modes was measured. This dependence is discussed in relation with recent calculations. The present data confirm/contradict some previous interpretations.

[Role of antibiotic therapy in diabetic foot management]

Antibiotic therapy is not the most important component in diabetic foot ulcer management which should be based on weight bearing avoidance and arterial revascularization. However antibiotic therapy is necessary in presence of extensive deep involvement or systemic signs of infection. Initial antimicrobial treatment depends on bacteria supposed origin. For patients not coming from hospital, the initial choice antibiotic is an amoxicillin/clavulanate agent because it offers optimal coverage for most pathogens involved in those diabetic foot lesions (gram positive cocci, gram negative and anaerobic organisms). For patients at high risk to be infected with nosocomially acquired pathogens, the initial antibiotic therapy must cover methicillin-resistant staphylococci, resistant pseudomonas aeruginosa or enterobacteriae. In all cases, when definitive reliable cultures are reported, initial antibiotic regimens should be revised to narrow the coverage to specific pathogens. In presence of osteomyelitis, a temporary combination of two agents which are known to reach high bone concentrations is necessary, and antibiotic therapy should be continued for at least two months. In other cases, antibiotic treatment duration depends on clinical out come.

[Surveillance of multiresistant bacteria: justification, role of the laboratory, indicators, and recent French data]

In France, several organizations have given priority status to programs aimed at controlling outbreaks of nosocomial infections due to multiresistant bacteria (MRB), most notably methicillin-resistant Staphylococcus aureus (MRSA) and extended-spectrum beta-lactamase-producing Enterobacteriaceae (ESBLE), thus recognizing the widespread distribution and marked pathogenic potential of MRB. To evaluate the impact of preventive measures, surveillance systems have been set up by bacteriology laboratories. These systems rest on a number of indicators: (1) the percentage of strains of a given bacterial species recovered from diagnostic specimens that were multiresistant; (2) the number of new patients (cases) with recovery of a MRB strain from at least one diagnostic specimen (or at least one screening specimen); (3) the incidence, or incidence density, of cases per 1000 hospital days or 100 admissions; (4) the distinction between cases acquired in and transported to the hospital or department. Studies conducted in France between 1990 and 1995 found that the percentage of Klebsiella pneumoniae that were multiresistant was around 20% overall and 25 to 35% among nosocomial strains, and that the prevalence and incidence of cases were about 0.1 to 0.3 per 100 admissions. The proportion of S. aureus strains exhibiting resistance to methicillin was 35 to 40% overall and 50% among nosocomial strains, and the prevalence and incidence of cases ranged from 0.5 to 1 per 100 admissions.

Expression and human chromosomal localization to 17q25 of the growth-regulated gene encoding the mitochondrial ribosomal protein MRPL12

Mitochondrial activity requires the expression of nuclear genes, whose products are part of multiproteic complexes leading to ATP production and delivery. We recently characterized a growth-activated mRNA encoding the human mitochondrial ribosomal MRPL12 protein, which is thought to act as a translational regulator of mitochondrial mRNAs. We show here that MRPL12 mRNA expression is enhanced in growth-stimulated cells as a result of transcriptional activation, a feature lost in transformed cell lines. MRPL12 mRNA is highly expressed in the colon, in which a reduction in mitochondrial activity was shown to be associated with tumor formation. The human MRPL12 protein is encoded by a unique gene located on chromosome 17 (q25-qter). As no predisposition to colon cancer linked to this chromosomal region was hitherto reported, the MRPL12 gene might be involved in the process of differentiation of colonic epithelial cells.

A delayed-early response nuclear gene encoding MRPL12, the mitochondrial homologue to the bacterial translational regulator L7/L12 protein

We have characterized a new delayed-early response mRNA encoding a 21-kDa product (MRPL12) that accumulates during the G1 phase of growth-stimulated cells. MRPL12 is the mammalian homologue to chloroplastic and bacterial L12 ribosomal proteins. Immunofluorescence microscopy and cell fractionation indicate a predominant mitochondrial localization in various mammalian cell lines. The NH2-terminal 49 amino acids are necessary and sufficient to target the protein within the mitochondria and are probably cleaved off during import. MRPL12 proteins associated in vitro and cofractionate with ribosomal structures, as is the case for prokaryotic L12 proteins. Expression of a dominant inhibitory truncated protein leads to a severe reduction in cell growth by inhibiting mitochondrial ATP production. MRPL12 is the first mammalian mitochondrial ribosomal protein to be characterized.

Growth-regulated expression of FKBP-59 immunophilin in normal and transformed fibroblastic cells

Expression of many primary response cellular genes is observed during the early stages of transition from a resting G0 state to DNA synthesis. To identify gene products implicated in long-term response to growth factors, we have isolated genes sequentially activated several hours after serum stimulation of fibroblastic CCL39 cells. We report here the characterization of one of them as encoding the immunophilin of 56-59 kDa (FKBP-59), a component of the steroid receptor complex. FKBP-59 is encoded in several mammalian species by a unique gene located within the transition protein 2 gene locus. FKBP-59 mRNA is ubiquitously expressed at various levels in human organs. FKBP-59 gene activation in CCL39 fibroblasts requires protein synthesis during the first 2 h of stimulation, a period of time during which proto-oncogenes such as c-fos or c-jun are expressed. FKBP-59 mRNA degrades upon serum withdrawal and accumulates in proportion to the mitogenic strength of various purified growth factors. Its expression is reduced in CCL39 mutant-transformed cells or cells able to grow in low serum-containing medium, suggesting that FKBP-59 might participate in the negative feedback control to cell proliferation.

Characterization of late response genes sequentially expressed during renewed growth of fibroblastic cells

Many proto-oncogenes are rapidly and transiently activated during the early stages of the cellular transition from a resting G0 state to the DNA synthesis (S) phase. To get better understanding of the gene complexity involved at later stages, we isolated, by cDNA cloning, and identified 17 genes that are activated sequentially during the period of time from proto-oncogene expression to the onset of DNA synthesis in the hamster CCL39 fibroblastic cell line. When protein synthesis is inhibited, induced expression of these genes is unaffected for 10 of them, enhanced for four, in a fashion similar to the immediate-early response genes, and inhibited for three, as observed for delayed early-response genes. In addition to rhoG, a new member of the ras homolog gene family (Vincent et al., 1992), cDNA sequencing indicated that six of them correspond to cytoskeletal proteins (alpha-tubulin, vascular alpha-actin and skeletal gamma-actin), extracellular matrix protein (thrombospondin), secreted protease (plasminogen activator inhibitor-1) and energy-linked transporter (mitochondrial proton/phosphate symporter). This overall survey shows that numerous differentially regulated gene activations are associated with the cell cycle progression, and suggests that proteins involved in cellular reshaping participate actively in the control of cellular growth.

Resistance to methicillin and virulence of Staphylococcus aureus strains in bacteriemic cancer patients

OBJECTIVE

To estimate the relation between resistance to methicillin and virulence in strains of Staph. aureus by estimating the survival at day 30.

DESIGN

Case control analysis.

SETTING

Inpatients at a major Cancer Referral Center.

PATIENTS

21 patients with methicillin-resistant Staph. aureus (MRSA) bactaeremia and 45 patients with methicillin-susceptible Staph. aureus (MSSA) bactaeremia, all treated with vancomycin.

MEASUREMENTS AND MAIN RESULTS

Fewer MRSA than MSSA patients were neutropenic (p = 0.04), but more MRSA patients were hospitalized in intensive care units (p = 0.03), had had surgical episodes (p = 0.06). MRSA patients also had more microbiological samples cultured (p = 0.007). The outcome of the bacteriemic episodes in 14 MRSA and 14 MSSA patients matched for these four factors showed that blood cultures from MRSA patients remained positive significantly longer (p = 0.04), but that survival and length of hospital stay were not significantly different.

CONCLUSIONS

These results do not indicate that methicillin-resistance in Staph. aureus is associated with increased virulence.

S26 ribosomal protein RNA: an invariant control for gene regulation experiments in eucaryotic cells and tissues

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Retrovirus-mediated gene transfer of a human c-fos cDNA into mouse bone marrow stromal cells

A cDNA encoding a complete human c-fos protein was isolated and inserted into two different murine MoMuLV-derived recombinant retroviruses allowing expression of c-fos protein in different cell types. One c-fos-expressing retrovirus, chosen for its ability to express high levels of proteins in fibroblast-like cells, was shown to potentiate long-term cultures of mouse bone marrow stromal cells in vitro and therefore constitutes a potential tool for immortalizing such cells. Moreover, when tested in an in vitro differentiation assay, stromal cells constitutively expressing c-fos favor the granulocyte differentiation of hematopoietic precursors. Interestingly, retroviruses expressing v-src and v-abl oncogenes, included as controls in our experiments, do not produce any detectable effects, whereas those expressing polyoma virus middle T antigen facilitate long-term growth in vitro of stromal cells that favor the macrophage differentiation pathway of bone marrow stem cells. Our observation supports the idea that constitutive expression of some oncogenes, including c-fos and polyoma virus middle T antigen, may influence cytokine production by bone marrow stromal cells.

Renal complications of intravesical bacillus Calmette-Guérin therapy

We report 3 patients who developed signs of systemic infection and renal insufficiency after intravesical bacillus Calmette-Guérin (BCG) instillations for a bladder cancer. Renal biopsy showed tubulo-interstitial nephritis with or without epithelioid granulomas in 2 cases, and mesangial glomerulonephritis in the last case. All patients had granulomatous hepatitis in association. It seems that hematogenous dissemination via a traumatic instillation of BCG and/or an immune-complex mechanism may have contributed to the renal damage, which was only partially reversible in 2 patients.

MoMuLV-derived self-inactivating retroviral vectors possessing multiple cloning sites and expressing the resistance to either G418 or hygromycin B

To facilitate cloning procedures in recombinant murine leukemia virus-derived retroviruses, we have constructed vectors that both carry a polylinker with multiple restriction sites and express resistance to either G418 or hygromycin B. Our vectors are self-inactivating retroviruses that suppress interferences between LTR enhancers and internal promoters and avoid transcriptional stimulation of host cell genes. They can also be used as expression vectors in direct transfection assays, since no translation initiation codon lies between the 5' LTR and the cloning polylinker.

AUUUA motifs are dispensable for rapid degradation of the mouse c-myc RNA

Sequence determinants responsible for c-myc RNA rapid turn-over are localized within the 3' non-coding region which is mainly characterized by the presence of two polyadenylation signals and a high content in A and U. Although the AUUUA/UUAUUUA motif is commonly thought to specify a whole class of unstable RNAs coding for various onco-proteins and cytokines, site-directed mutagenesis showed that both of the two such sequences found in the mouse c-myc RNA are dispensable for rapid RNA degradation. Although less efficient than the whole 3' non-coding region, the last 50 nucleotides of c-myc RNA, mainly made up of U and A and devoid of AUUUA/UUAUUUA motif, are sufficient to confer instability to the coding sequence.

[Obstructive renal lithiasis, hypercalcemia, parathyroid adenoma and term pregnancy. Report of a case]

The authors report an observation of primitive hyperparathyroidism by adenoma diagnosed at the time of a bilateral urinary lithiase, obstructive on the left, with hypercalcemia in young pregnant woman near of the term.

The muridae glyceraldehyde-3-phosphate dehydrogenase family

Although only one gene is known to be functional, numerous glyceraldehyde-3-phosphate dehydrogenase (GAPDH) related sequences are scattered throughout Mus musculus and Rattus rattus genomes. In this report we show that: (1) GAPDH pseudogenes are repeated to comparable extents, at least 400 copies, in 12 other Muridae species; (2) the complete, or nearly so, sequence of GAPDH messenger RNA is amplified, and a high proportion, if not all of these copies, are intronless; (3) GAPDH pseudogenes are preferentially located in heavily methylated and DNAse I-insensitive regions of chromatin; and (4) the presence of atypical GAPDH-related mRNAs in different cellular contexts raises the possibility that more than one GAPDH gene is transcribed.

[Use of salbutamol in the treatment of severe hyperkalemia in hemodialysed patients]

The possibility of obtaining a rapid fall of kalaemia in patients with renal failure under haemodialysis by injecting salbutamol intravenously in doses of 0.5 mg over 15 minutes was tested in 11 subjects. Kalaemia fell by 1.08 +/- 0.30 mmol in 30 minutes, 75 per cent of the effect being obtained at the end of the infusion. Malaise with tachycardia was frequent but always transient. Thus, a rapid infusion of salbutamol seems to be well tolerated and effective against hyperkalaemia, provided two contra-indications are observed: coronary disease and treatment with beta-blockers.

Role of RNA structures in c-myc and c-fos gene regulations

Proto-oncogenes c-myc and c-fos are subjected to a complex set of controls operating both at the transcriptional and post-transcriptional levels. We report here that: (i) antisense transcription occurs at the murine c-myc locus. However, its biological significance remains to be established; (ii) transcription of both genes is regulated in various situations by a block to elongation of nascent RNA chains. In the case of c-myc, the blockade involves a RNA structure whose nature remains unknown; (iii) elements responsible for the high degree of instability of c-myc and c-fos mRNAs reside in their 3' non-coding regions. A U-rich region, reminiscent of that present in the granulocyte-monocyte colony-stimulating factor mRNA destabilizer, is likely to be involved in the rapid degradation of c-fos mRNA; (iv) exon 1 substitution by intron 1-derived sequences lessens or negates the effect of the 3' destabilizer in abnormal c-myc RNAs from Burkitt's lymphomas and mouse plasmacytomas.

Sequence determinants of c-myc mRNA turn-over: influence of 3' and 5' non-coding regions

Normal c-myc RNAs are very unstable with a half-life of less than 30 min whereas those rearranged in 5', as found in Burkitt's lymphomas and mouse plasmacytomas, are significantly more stable. To learn about the sequence determinants controlling their turnover, we have studied naturally occurring and artificially constructed c-myc RNAs rearranged in 5' or 3'. The first conclusion is that sequences necessary for rapid c-myc RNAs turnover are localized in their 3' untranslated region. The second conclusion is that stabilization of truncated c-myc RNAs in tumors does not result from deletion of the non-coding first exon but rather from its replacement by intronic and/or exogenous sequences. This latter conclusion rests on two lines of evidence: (i) deleting the 5' rearranged sequences from the relatively stable MOPC 315 RNA restores its complete instability (pSV c-myc 1); (ii) reciprocally, appending intron 1 sequences 5' to otherwise unstable germline c-myc exons 2 and 3 have a dramatic stabilizing effect (pIM 0).

Transcriptional and post-transcriptional regulation of c-myc expression during the differentiation of murine erythroleukemia Friend cells

c-myc RNA rapidly decreases to barely detectable levels in Friend erythroleukemia cells induced to differentiate upon the addition of dimethylsulfoxide. We show here that c-myc gene is down-regulated both at the transcriptional level presumably by a block in the elongation of primary transcripts and at the post-transcriptional level by an increase in the degradation of its mRNA.

Various rat adult tissues express only one major mRNA species from the glyceraldehyde-3-phosphate-dehydrogenase multigenic family

We have isolated and sequenced a full-length cDNA clone encoding rat glyceraldehyde-3-phosphate-dehydrogenase (GAPDH, E.C.1.2.1.12). The entire mRNA is 1269 nucleotides long exclusive of poly(A) and contains respectively 71 and 196 bases of 5' and 3' non-coding regions. Primer extension as well as S1 nuclease protection experiments clearly established that a single (or at least a highly prominent) GAPDH mRNA species is expressed in all rat tissues examined. This sequence allowed the determination of the hitherto unknown primary structure of rat GAPDH which is 333 aminoacids long. Comparison between GAPDH sequences from rat, man and chicken revealed a high degree of sequence conservation at both nucleotide and protein levels.

Characterization of the transcription products of glyceraldehyde 3-phosphate-dehydrogenase gene in HeLa cells

We have partially purified the messenger RNA coding for glyceraldehyde-3-phosphate dehydrogenase (GAPDH, EC 1.2.1.12) from HeLa cells and obtained a cDNA clone containing part of its sequence. Using this clone to probe electrophoregrams of RNA transferred to nitrocellulose, we have investigated the characteristics of nuclear and cytoplasmic transcripts in these cells. In the cytoplasm, nature GAPDH mRNA was detected in Northern blots as an intense band, apparently unique, of approximately 1400 nucleotides. The half-life of this mRNA was determined both from the decay kinetics, after a chase with actinomycin D, and from the labeling kinetics during an accumulation experiment. Both kinds of experiments yielded a half-life value of about 8 h, while the accumulation experiment indicated that steady-state GAPDH mRNA amounted to about 1.6% of cytoplasmic poly(A)-rich RNA. Much longer species, likely to be restricted to the nucleus, were also detected in RNA extracted from total cells. At least three discrete species of 1600, 4000, 5800 and 6800 bases were observed above a trailing background extending up to about 8000 bases. This value is commensurate with a functional size of the GAPDH transcription unit in the order of 13000 bases, which we determined by measuring the size of the ultraviolet inactivation target. Until direct evidence can be obtained at the genomic level, the present results provide the first clue to the existence of introns, presumably at least four, in a GAPDH gene from a higher eucaryote.