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The last two amino acids in the nascent peptide influence translation termination in E. coli (Mottagui-Tabar et al., 1994; Bj?rnsson et al., 1996). We have compared the effects on termination in Escherichia coli, Bacillus subtilis and Salmonella typhimurium obtained by varying the -1 and -2 codons upstream of the weak UGAA stop signal. The peptide effect from the penultimate amino acid on translation termination in B. subtilis is similar to that seen in E. coli (with 66.5% RF-2 amino acid sequence similarity), whereas the influence in S. typhimurium (with 95.3% similarity to E. coli) is weaker. The effect of changing the -1 codon (P-site) is weaker in S. typhimurium as compared to those in E. coli and B. subtilis. RF-2s from E. coli and S. typhimurium have a threonine or alanine at position 246, respectively. This amino acid exchange in RF-2 can explain the difference in efficiency and toxicity during overexpression when E. coli and S. typhimurium are compared (Uno et al., 1996). However, B. subtilis RF-2 also has an alanine at that position, yet the sensitivity to the nascent peptide is similar to that in E. coli. Thus, the amino acid difference at position 246 in the RF-2 sequences cannot explain why termination in E. coli and B. subtilis is similar in peptide sensitivity while being different from that in S. typhimurium. Sequence alignments of RF-2 from the three bacteria show other regions of the molecule that could be involved in the functional interactions with the C-terminal end of the nascent peptide.  相似文献   
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https://doi.org/10.2516/ogst:1997021  相似文献   
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Aggregating suspensions generally separate into a clear supernatant and a voluminous gelled sediment. The suspension remains homogeneous (i. e. a gel stable under gravity forms) only when the volume fraction of particles exceeds a given value Phi**. The present study is devoted to the determination of Phi**. A simplified model describing the gel equilibrium has been developed and its validity is checked comparing its predictions to systematic measurements of the sediment volume performed on calcium carbonate suspensions. Applying this model to the prediction of Phi**, we show that Phi** is not a characteristic of the physico-chemical system but depends on the height of the sample, its aspect ratio and friction between the gel and the side wall. For large (respectively small) aspect ratios, we find that Phi** is a power law function of the width (respectively the height) of the sample involving an exponent 1/(K - 1) which is related to the dependence of the yield stress on the volume fraction of the suspension.https://doi.org/10.2516/ogst:1997018  相似文献   
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New 4th-generation synchrotron sources,with their increased brilliance,promise to greatly improve the performances of coherent X-ray microscopy.This perspective...  相似文献   
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The main points of a workshop on the place of clinical trials in the memory clinics in France are reproduced schematically. The efficiency of these centres has been tested at the time of the numerous clinical trials performed in France on Alzheimer's disease. In parallel, several difficulties have been pointed out: inhomogeneity of the technical approaches, official role of psychologists in the hospital teams, integration of clinical research to individual care. A particular effort should be oriented towards specific research on the different types of dementia, on early stages, on information for both media and authorities as well as on specific technical and methodological problems.  相似文献   
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Lithium has been utilized to enhance the plasma performance for a variety of fusion devices such as TFTR, CDX-U and NSTX. Lithium in both the solid and liquid states has been studied extensively for its role in hydrogen retention and reduction in sputtering yield. A liquid lithium diverter (LLD) was recently installed in the National Spherical Torus Experiment (NSTX) fusion reactor to investigate lithium applications for plasma-facing surfaces (PFS). Representative samples of LLD material were exposed to lithium depositing and simulated plasma conditions offline at Purdue University to study changes in surface chemical functionalities of Mo, O, Li and D. X-ray photoelectron spectroscopy (XPS) conducted on samples revealed two distinct peak functionalities of lithiated porous molybdenum exposed to deuterium irradiation. The two-peak chemical functionality noticed in porous molybdenum deviates from similar studies conducted on lithiated graphite; such deviation in data is correlated to the complex surface morphology of the porous surface and the correct “wetting” of lithium on the sample surface. The proper lithium “wetting” on the sample surface is essential for maximum deuterium retention and corresponding LLD pumping of deuterium.  相似文献   
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Examined interrelationships among sex, race, drug use patterns, and personality variables in 84 chronic users of illicit drugs (mean age 24.3 yrs). Ss were administered the MMPI, the Sensation Seeking Scale, and the Shipley-Institute of Living Scale for Measuring Intellectual Impairment and were interviewed using the Background Information Questionnaire. Comparisons were made between sex and ethnic subgroups on personality and drug use variables using analysis of covariance and chi-square procedures for Ss classified into high-, medium-, and low-sensation-seeking groups. Blacks were characterized by lower levels of sensation seeking, less psychopathology, use of fewer drug categories, and later drug use than Whites. Use and personality patterns among women differed little from those of men. Levels of sensation seeking were related to specific personality constellations, number of drug categories used, and motive for first alcohol use. (14 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
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