Showing papers by "University of Erlangen-Nuremberg published in 1994"

Mechanisms underlying expression of tn10 encoded tetracycline resistance

Abstract: Tetracycline-resistance determinants encoding active efflux of the drug are widely distributed in gram-negative bacteria and unique with respect to genetic organization and regulation of expression. Each determinant consists of two genes called tetA and tetR, which are oriented with divergent polarity, and between them is a central regulatory region with overlapping promoters and operators. The amino acid sequences of the encoded proteins are 43-78% identical. The resistance protein TetA is a tetracycline/metal-proton antiporter located in the cytoplasmic membrane, while the regulatory protein TetR is a tetracycline inducible repressor. TetR binds via a helix-turn-helix motif to the two tet operators, resulting in repression of both genes. A detailed model of the repressor-operator complex has been proposed on the basis of biochemical and genetic data. The tet genes are differentially regulated so that repressor synthesis can occur before the resistance protein is expressed. This has been demonstrated for the Tn10-encoded tet genes and may be a common property of all tet determinants, as suggested by the similar locations of operators with respect to promoters. Induction is mediated by a tetracycline-metal complex and requires only nanomolar concentrations of the drug. This is the most sensitive effector-inducible system of transcriptional regulation known to date. The crystal structure of the TetR-tetracycline/metal complex shows the Tet repressor in the induced, non-DNA binding conformation. The structural interpretation of many noninducible TetR mutants has offered insight into the conformational changes associated with the switch between inducing and repressing structures of TetR. Tc is buried in the core of TetR, where it is held in place by multiple contacts to the protein.

SiC devices: physics and numerical simulation

Abstract: The important material parameters for 6H silicon carbide (6H-SiC) are extracted from the literature and implemented into the 2-D device simulation programs PISCES and BREAKDOWN and into the 1-D program OSSI Simulations of 6H-SiC p-n junctions show the possibility to operate corresponding devices at temperatures up to 1000 K thanks to their low reverse current densities. Comparison of a 6H-SiC 1200 V p-n/sup -/-n/sup +/ diode with a corresponding silicon (Si) diode shows the higher switching performance of the 6H-SiC diode, while the forward power loss is somewhat higher than in Si due to the higher built-in voltage of the 6H-SiC p-n junction. This disadvantage can be avoided by a 6H-SiC Schottky diode. The on-resistances of Si, 3C-SiC, and 6H-SiC vertical power MOSFET's are compared by analytical calculations. At room temperature, such SiC MOSFET's can operate up to blocking capabilities of 5000 V with an on-resistance below 0.1 /spl Omega/cm/sup 2/, while Si MOSFET's are limited to below 500 V. This is checked by calculating the characteristics of a 6H-SiC 1200 V MOSFET with PISCES. In the voltage region below 200 V, Si is superior due to its higher mobility and lower threshold voltage. Electric fields in the order of 4/spl times/10/sup 6/ V/cm occur in the gate oxide of the mentioned 6H-SiC MOSFET as well as in a field plate oxide used to passivate its planar junction. To investigate the high frequency performance of SiC devices, a heterobipolartransistor with a 6H-SiC emitter is considered. Base and collector are assumed to be out of 3C-SiC. Frequencies up to 10 GHz with a very high output power are obtained on the basis of analytical considerations. >

Laser triangulation: fundamental uncertainty in distance measurement

Abstract: We discuss the uncertainty limit in distance sensing by laser triangulation. The uncertainty in distance measurement of laser triangulation sensors and other coherent sensors is limited by speckle noise. Speckle arises because of the coherent illumination in combination with rough surfaces. A minimum limit on the distance uncertainty is derived through speckle statistics. This uncertainty is a function of wavelength, observation aperture, and speckle contrast in the spot image. Surprisingly, it is the same distance uncertainty that we obtained from a single-photon experiment and from Heisenberg's uncertainty principle. Experiments confirm the theory. An uncertainty principle connecting lateral resolution and distance uncertainty is introduced. Design criteria for a sensor with minimum distanc uncertainty are determined: small temporal coherence, small spatial coherence, a large observation aperture.

Structure of the Tet repressor-tetracycline complex and regulation of antibiotic resistance

Abstract: The most frequently occurring resistance of Gram-negative bacteria against tetracyclines is triggered by drug recognition of the Tet repressor. This causes dissociation of the repressor-operator DNA complex and enables expression of the resistance protein TetA, which is responsible for active efflux of tetracycline. The 2.5 angstrom resolution crystal structure of the homodimeric Tet repressor complexed with tetracycline-magnesium reveals detailed drug recognition. The orientation of the operator-binding helix-turn-helix motifs of the repressor is inverted in comparison with other DNA binding proteins. The repressor-drug complex is unable to interact with DNA because the separation of the DNA binding motifs is 5 angstroms wider than usually observed.

Tissue expression of inducible nitric oxide synthase is closely associated with resistance to Leishmania major.

Abstract: Previous studies with inhibitors of inducible nitric oxide synthase (iNOS) suggested that high-output production of nitric oxide (NO) is an important antimicrobial effector pathway in vitro and in vivo. Here, we investigated the tissue expression of iNOS in mice after infection with Leishmania major. Immunohistochemical staining with an iNOS-specific antiserum revealed that in the cutaneous lesion and draining lymph nodes (LN) of clinically resistant mice (C57BL/6), iNOS protein is found earlier during infection and in significantly higher amounts than in the nonhealing BALB/c strain. Similar differences were seen on the mRNA level as quantitated by competitive polymerase chain reaction. Anti-CD4 treatment of BALB/c mice not only induced resistance to disease, but also restored the expression of iNOS in the tissue. In situ, few or no parasites were found in those regions of the skin lesion and the draining LN which were highly positive for iNOS. By double labeling experiments, macrophages were identified as iNOS expressing cells in vivo. In the lesions of BALB/c mice, cells staining positively for transforming growth factor beta (TGF-beta), a potent inhibitor of iNOS in vitro, were strikingly more prominent than in C57BL/6, whereas no such difference was found for interleukin 4 or interferon gamma (IFN-gamma). In vitro, production of NO was approximately threefold higher in C57BL/6 than in BALB/c macrophages after stimulation with IFN-gamma. We conclude that the pronounced expression of iNOS in resistant mice is an important mechanism for the elimination of Leishmania in vivo. The relative lack of iNOS in susceptible mice might be a consequence of macrophage deactivation by TGF-beta and reduced responsiveness to IFN-gamma.

Fracture Behavior of Polymers

Abstract: Fracture analysis is complicated for polymers since, besides of temperature and time dependence, there are involved effects from plastification, chain orientation and adiabatic temperature rise. It is the aim of this section to describe several fracture processes which are specific of polymers. Fracture behavior is determined experimentally by the mode and time profile of loading. Stress- and strain controlled loading yields different behavior as well as loading in tension, compression or shear (torsion). Compressive strength is higher than tensile strength; shear strength is the lowest one.

Different patterns of hyperalgesia induced by experimental inflammation in human skin

Abstract: Different types of hyperalgesia were studied after experimental induction of inflammation in small skin areas of healthy volunteers either by topical application of capsaicin solution (1% in 70% ethanol) or by briefly freezing a skin area of similar size to -28 degrees C Sensory tests were performed 30 min after capsaicin application and 22 h after freeze lesions Heat pain thresholds were lowered after both treatments, probably due to nociceptor sensitization Hyperalgesia to four types of mechanical stimulation was studied (i) Hyperalgesia to punctate stimuli was encountered at the skin site directly affected by the noxious chemical or freeze stimulus (1 degree zone) and in the surrounding skin (2 degrees zone) in both models though the area of 2 degrees hyperalgesia to punctate stimuli after freezing was smaller than after capsaicin (ii) Hyperalgesia to gently brushing the skin was prominent after capsaicin in 1 degree and 2 degrees zone, but almost absent after freezing It was concluded that both hyperalgesia to punctate stimuli and brush-evoked pain are due to central nervous plasticity changes rather than nociceptor sensitization As revealed by differential nerve blocks, brush-evoked pain is mediated by low threshold mechanosensitive A beta-fibres, whilst hyperalgesia to punctate stimuli can be elicited when only C-fibres conduct In contrast to hyperalgesia to punctate stimuli it requires continuous background discharges in nociceptor units (iii) Pressure hyperalgesia to tonic stimulation with a blunt probe was encountered in the 1 degree zone of both types of inflammation and is probably due to recruitment of sensitized nociceptor units (iv) Impact hyperalgesia was studied by shooting small bullets against the skin at predetermined velocities It was found in the 1 degree zone after freezing and absent in the capsaicin model Differential nerve blocks revealed that it is probably mediated by sensitized C-fibres In conclusion, different types of inflammatory changes may result in characteristic different patterns of hyperalgesia

Dispersive interferometric profilometer

Abstract: The usual automated interferometric profilometers suffer from phase-unwrapping problems. We discuss a one-dimensional method for the absolute determination of the path difference in interferometers to obtain unique surface profiles with high accuracy.

A chimeric transactivator allows tetracycline-responsive gene expression in whole plants

Abstract: Summary The chimeric transcriptional activator tTA, a fusion between the Tn 10 encoded Tet repressor and the activation domain of the Herpes simplex virion protein VP16, was stably expressed in transgenic tobacco plants. It stimulates transcription of the β-glucuronidase (gus) gene from an artificial promoter consisting of 7 tet operators and a TATA-box. Tetracycline, which Interferes with binding of tTA to operator DNA, reduces gus expression over several orders of magnitude. This stringency of regulation suggests that the system can be used to construct transgenic plants encoding a potentially lethal gene product. Furthermore, the specific and fast inactivation of tTA allows study of the stability of RNAs and proteins.

Relationships between the radon-wigner and fractional fourier transforms

Abstract: Two recently described transforms are shown to be related. The Radon–Wigner transform is the squared modulus of the fractional Fourier transform. This new theorem may serve to translate signal and image processing results between different signal representations. Some consequences regarding moments are presented, including a new fractional-Fourier-transform uncertainty relation. Implications for processing are suggested.

Optical operations on wave functions as the Abelian subgroups of the special affine Fourier transformation.

Abstract: The special affine Fourier transformation (SAFT) is a generalization of the fractional Fourier transformation (FRT) and represents the most general lossless inhomogeneous linear mapping, in phase space, as the integral transformation of a wave function. Here we first summarize the most well-known optical operations on light-wave functions (i.e., the FRT, lens transformation, free-space propagation, and magnification), in a unified way, from the viewpoint of the one-parameter Abelian subgroups of the SAFT. Then we present a new operation, which is the Lorentz-type hyperbolic transformation in phase space and exhibits squeezing. We also show that the SAFT including these five operations can be generated from any two independent operations.

Graded-index fibers, Wigner-distribution functions, and the fractional Fourier transform.

Abstract: Two definitions of a fractional Fourier transform have been proposed previously. One is based on the propagation of a wave field through a graded-index medium, and the other is based on rotating a function's Wigner distribution. It is shown that both definitions are equivalent. An important result of this equivalency is that the Wigner distribution of a wave field rotates as the wave field propagates through a quadratic graded-index medium. The relation with ray-optics phase space is discussed.

UL69 of human cytomegalovirus, an open reading frame with homology to ICP27 of herpes simplex virus, encodes a transactivator of gene expression.

Abstract: The UL69 open reading frame of human cytomegalovirus (HCMV) is homologous to the immediate-early protein ICP27 of herpes simplex virus, an essential viral regulatory protein involved in the transition from early to late gene expression. Genes with homology to ICP27 have been detected in all subclasses of herpesviruses so far. While the respective proteins in alpha- and gammaherpesviruses have been defined as trans-regulatory molecules, nothing is known about these genes in betaherpesviruses. This study was therefore undertaken in order to investigate expression from the UL69 gene locus of HCMV. Northern (RNA) blot experiments revealed a complex pattern of transcripts that changed during the time course of the HCMV replicative cycle: two transcripts of 2.7 and 3.5 kb that were regulated differentially could be detected as early as 7 h after infection. However, these transcripts could not be detected in the presence of cycloheximide. Additional, larger transcripts were present exclusively at late times after infection. To analyze protein expression from the UL69 gene region, the UL69 open reading frame was expressed as a histidine-tagged protein in Escherichia coli. A specific antiserum was generated and used to detect the UL69 protein in HCMV-infected cells which revealed its localization within the intranuclear inclusions that are characteristic for HCMV infection. In cotransfection experiments, an HCMV true late promoter could not be activated by UL69, whereas an early promoter and several heterologous promoters were stimulated about 10-fold. Complementation studies showed that the UL69 protein cannot substitute for ICP27 in the context of the HSV infection, suggesting functional differences between these two proteins. In summary, these experiments define a novel regulatory protein encoded by HCMV that is expressed as an early-late gene and appears to exert a broad stimulatory effect on gene expression.

Organ-sparing treatment of advanced bladder cancer: a 10-year experience.

Abstract: Purpose: Radical cystectomy is considered as standard therapy for muscle-invasive bladder cancer. We present 10-year results of bladder-sparing treatment by conservative surgery and radiotherapy ± chemotherapy. Methods and Materials: From 1982 through 1991, 245 consecutive patients, mean age 66 years, with invasive bladder cancer (T2-3 or poor prognostic T1, no distant metastases) entered a prospective protocol with the objective of bladder preservation. Treatment consisted of transurethral resection (complete, if possible) and definitive radiotherapy with 56 Gy maximum dose (50.4 Gy minimum target dose) in 28 fractions. Since 1985, 139 patients received a simultaneous chemotherapy on 5 days in the first and fifth treatment week with either 25 mg/m2 cisplatin daily (79 patients) or 65 mg/m2 carboplatin (60 patients). Cystectomy was performed as salvage treatment for residual or recurrent invasive disease. The median follow-up at the date of analysis (12-31-92) was 5.9 years. Results: The overall survival was 47% after 5 years and 26% after 10 years. The 5-year survival according to the initial T-category was 60% for T1 (44 patients), 64% for T2 (47 patients), 43% for T3 (127 patients), and 16% for T4 (23 patients). The most important single prognostic factor was the amount of residual tumor after TUR (5-year survival 80% after R0, 53% after R1, and 31% after R2 resection, p < 0.01). Chemotherapy increased the rate of complete remission, but had no impact on 5-year survival (52% vs. 50%). Fifty-three salvage cystectomies were performed, all without severe complications, and 192 patients (79%) maintained a normal functioning bladder. The bladder preservation rate in 5-year survivors was 83%. Conclusions: Organ-sparing treatment of advanced bladder cancer by transurethral surgery and definitive radiotherapy or radiochemotherapy is feasible and effective. The survival in this series is as good as in any comparable cystectomy series. Eighty-three percent of long-term survivors maintained their functioning bladders.

Lipoteichoic acid and lipids in the membrane of Staphylococcus aureus.

Abstract: Lipoteichoic acids (LTAs), glycolipids and, less wide-spread, teichoic acids (TAs) are characteristic components of the cell wall-membrane complex in a large group of gram-positive bacteria (for references see [ 17, 18]). After a period of hypotheses for essential functions [46], LTA and TA were for a while considered as more or less secondary cellular components, but this view is now changing again. There is clear evidence that TA is indispensable for the viability of Bacillus subtilis [50]. In Staphylococcus aureus, TA is needed for normal growth [10] and becomes indispensable for growth under extreme conditions (W. Fischer, unpublished data). Notably, no mutants lacking LTA have yet been detected on chemical mutagenesis, either in S. aureus (W. Fischer and K. Leopold, unpublished data) or in Lactobacillus casei [51]. For these reasons the biosynthetic pathways of TA and LTA have gained interest as possible targets for new antibiotics. This brief overview is focussed on LTA, TA and membrane lipids of S. aureus but biosynthetic and functional aspects of these components are similar in other gram-positive bacteria [ 17, 18].

The Properties of Isolated Magnetic Vortices

Abstract: Isolated magnetic vortices are stabilized by an antisymmetric exchange interaction, the so-called Dzyaloshinsky interaction, which can be represented as an energy contribution linear in the first spatial derivatives of the magnetization vector. In contrast, vortex lines are demonstrated to be unstable in the bulk of regular uniaxial ferromagnets. They collapse spontaneously under the influence of anisotropy or an applied magnetic field. In reduced units the differential equation for isolated vortices contains two parameters: the reduced magnetic field h along the crystal axis and the material parameter which describes the relative contribution of the Dzyaloshinsky interaction term. Isolated vortices turn out to be always metastable for large fields, independent of as long as this parameter is positive. At low or negative fields they become unstable by two different mechanisms depending on the -value, but altogether these micromagnetic structures turn out to be stable in a remarkably wide range of parameters. At the end possible applications are considered.

The E6/E7 promoter of extrachromosomal HPV16 DNA in cervical cancers escapes from cellular repression by mutation of target sequences for YY1.

Abstract: Human papillomavirus type 16 (HPV16) induces squamous intraepithelial lesions of the cervical mucosa which may develop into invasive cancer. The expression of viral oncogenes in advanced neoplasias appears increased relative to the proliferating cell layers of low grade lesions raising questions about molecular mechanisms of deregulation of transcription. In a lymph node metastasis of a cervical cancer, we observed full-length HPV16 plasmids and molecules with a small deletion, which was mapped to the long control region (LCR). Both wild type and shortened LCR were amplified by PCR, cloned into the promoter test plasmid pBLCAT6 and sequenced to identify a 107 bp deletion from position 7794 to 7901 in the short LCR. CAT expression in cervical cancer-derived HT3, SiHa and CaSki cells appeared 5- to 6-fold increased under the control of the short LCR. This could be traced back to elevated levels of mRNA initiated at the viral oncogene promoter. A slight further increase in CAT expression was noted in the presence of the HPV16 E2 protein which is probably due to the deletion of one E2 binding site and consequent relief from E2 repression. Computer-assisted sequence analysis and band-shift experiments with purified YY1 protein and wild type or mutated oligonucleotides identified four binding sites for this cellular transcriptional repressor within the promoter-proximal segment of the HPV16 LCR, three of which were removed by the deletion. A LCR fragment comprising these YY1 binding sites was cloned in front of the heterologous thymidine kinase gene promoter and suppressed CAT expression 3- to 4-fold.(ABSTRACT TRUNCATED AT 250 WORDS)

Residual tumor (R) classification and prognosis.

Abstract: The tumor status following treatment is described by the residual tumor (R) classification: R0, no residual tumor; R1, microscopic residual tumor; R2, macroscopic residual tumor. Residual tumor may be found in the area of primary tumor and its regional lymph nodes and/or at distant sites. The R classification reflects the effects of treatment and influences further treatment planning. Furthermore, the R classification is a strong predictor of prognosis. An acceptable long-term prognosis can be expected only in R0 patients. Although there exist clear correlations between stage and R classification the differences in prognosis of R0 versus R1,2 cannot be explained by differences in stage alone. The prognostic significance of R classification is demonstrated by respective data for non-small cell lung carcinoma, squamous cell carcinoma of oesophagus, gastric carcinoma, ductal adenocarcinoma of the pancreas, colorectal carcinoma, lung and liver metastases.