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1.
Abstract Clostridium perfringens alpha-toxin was produced in a protein-hyperproducing strain, Bacillus brevis 47, by cloning the gene into the constructed expression-secretion vector which has the multiple promoters and the signal peptide coding region of an outer cell wall protein gene. The amount of alpha-toxin produced by the B. brevis 47 transformant carrying the gene was approximately 10 times greater than that produced by a B. subtilis transformant carrying the toxin gene. Biological activities and the N-terminal amino acid sequence of the toxin secreted by the B. brevis 47 transformant were identical to those of wild-type alpha-toxin. 相似文献
2.
A Gram-positive Rhodococcus erythropolis strain S1 was shown to assimilate aromatic amino acids such as L-phenylalanine, L-tyrosine, L-tryptophan, D-phenylalanine, D-tyrosine and D-tryptophan, which were utilized not only as the sole carbon source but also as a suitable nitrogen source. The highest growth on these aromatic amino acids occurred at a temperature of 30°C. L-Phenylalanine, L-tyrosine and L-tryptophan degradative pathways would appear to be independent, and to be induced alternatively. The strain S1 also showed the ability to assimilate peptides which consisted of only L-phenylalanine and L-tyrosine. 相似文献
3.
Protective Effect of External Ca2+ on Elongation and the Intracellular Concentration of K+ in Intact Mung Bean Roots under High NaCl Stress 总被引:2,自引:0,他引:2
Nakamura Yoshiyuki; Tanaka Karo; Ohta Eiji; Sakata Makoto 《Plant & cell physiology》1990,31(6):815-821
The effects of Ca2+ in the external medium on intact mung beanroots under high NaCl stress were investigated. With increasingexternal concentrations of NaCl, mung bean roots showed suppressionof elongation and a decrease in the intracellular concentrationof K+. Addition of Ca2+ to the external medium alleviated theinhibition of root elongation under the high NaCl stress andmaintained a high intracellular concentration of K+ in the elongatingregion of the roots. This counter effect of Ca2+ against theNaCl stress on roots was correlated with the ratio of [Ca2+]/[Na+]2in the external medium. A value above 5.0 ? 104 mM1resulted in almost complete recovery of root elongation undervarious high concentrations of NaCl. Root elongation for 24h under NaCl stress was correlated with the extent to whichthe intracellular concentration of K+ was in excess of 10 mM.Maintenance of an adequate concentration of K+ in root cellsis essential for root elongation under salt stress. These findingsindicate that Ca2+ prevents the leakage of intracellular K+and thereby supports the elongation of roots under salt stress. (Received November 13, 1989; Accepted June 5, 1990) 相似文献
4.
Having discovered that the A domain of diphtheria toxin exhibits intrinsic nuclease activity (Chang, M. P., Baldwin, R. L., Bruce, B., and Wisnieski, B. J. (1989) Science 246, 1165-1168), we proceeded to examine the requirements for optimal enzymic expression. In vitro assays with linear double-stranded DNA demonstrated that optimal activity occurs at pH 7.5 and 37 degrees C. A characterization of the stringent cation-dependence of the reaction revealed increasing activity with increasing Mn2+ up to 30 mM. In contrast, activity levels with Ca2+ or Zn2+ alone peaked at 100 microM and with Mg2+ alone at 1 mM. The Zn2(+)- and Mg2(+)-stimulated activities appear to be dependent on trace amounts of Ca2+. Indeed, inclusion of 2 mM Ca2+ plus 3 mM Mg2+ in the reaction buffer promoted a high level of DNA cleavage even though very little cleavage was seen with either cation alone at 2-3 mM. Addition of 20-200 mM NaCl or KCl caused progressive inhibition. Detection of diphtheria toxin nuclease activity under physiologically relevant conditions suggests that it may be operative in vivo and supports our contention that diphtheria toxin-induced cytolysis is not a simple consequence of protein synthesis inhibition, but rather the final step in a cytolytic pathway linked to chromosomal integrity. 相似文献
5.
Xiang Liu Zhenghong Wang Chenyu Huang Manru Li Farkhanda Bibi Shurong Zhou Akihiro Nakamura 《Ecological Entomology》2020,45(3):547-554
1. Predator–prey interactions, especially those involving herbivorous insects, are of great importance in maintaining biodiversity. Predation pressure varies temporally in response to prey availability and activity. However, little is known about the patterns and drivers of fluctuations in predation pressure at fine temporal scales. 2. Artificial caterpillars (placed on plant leaves at breast height) were used to assess changes in predation pressure across four time intervals of the day in a monsoonal tropical rainforest in south-west China. The study examined how assemblage composition of arboreal ants, the dominant predators, changed across the same time intervals. The potential linkages between biotic (arboreal ants) and abiotic (temperature and light intensity) factors with predation rate were evaluated. 3. Predation rate on caterpillars during the early part of the night (19.00–01.00 hours) was significantly higher than in the morning, afternoon, or late night. Ant assemblage composition, rather than species richness or total abundance, best explained the variations in predation rate on artificial caterpillars. 4. The results help to strengthen understanding of trophic interactions by demonstrating that predation pressure fluctuates at finer timescales than previously tested, and that a particular set of ant species may play major roles in predation on caterpillars and possibly other organisms. 相似文献
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Takahiro Watanabe Yohei Narita Masahiro Yoshida Yoshitaka Sato Fumi Goshima Hiroshi Kimura Takayuki Murata 《Journal of virology》2015,89(19):10120-10124
Epstein-Barr virus (EBV) is a gammaherpesvirus, associated with infectious mononucleosis and various types of malignancy. We focused here on the BDLF4 gene of EBV and identified it as a lytic gene, expressed with early kinetics. Viral late gene expression of the BDLF4 knockout strain was severely restricted; this could be restored by an exogenous supply of BDLF4. These results indicate that BDLF4 is important for the EBV lytic replication cycle, especially in late gene expression. 相似文献
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10.
The oxygen cost of transport per unit distance (CoT; mL·kg-1·km-1) shows a U-shaped curve as a function of walking speed (v), which includes a particular walking speed minimizing the CoT, so called economical speed (ES). The CoT-v relationship in running is approximately linear. These distinctive walking and running CoT-v relationships give an intersection between U-shaped and linear CoT relationships, termed the energetically optimal transition speed (EOTS). This study investigated the effects of subtracting the standing oxygen cost for calculating the CoT and its relevant effects on the ES and EOTS at the level and gradient slopes (±5%) in eleven male trained athletes. The percent effects of subtracting the standing oxygen cost (4.8 ± 0.4 mL·kg-1·min-1) on the CoT were significantly greater as the walking speed was slower, but it was not significant at faster running speeds over 9.4 km·h-1. The percent effect was significantly dependent on the gradient (downhill > level > uphill, P < 0.001). The net ES (level 4.09 ± 0.31, uphill 4.22 ± 0.37, and downhill 4.16 ± 0.44 km·h-1) was approximately 20% slower than the gross ES (level 5.15 ± 0.18, uphill 5.27 ± 0.20, and downhill 5.37 ± 0.22 km·h-1, P < 0.001). Both net and gross ES were not significantly dependent on the gradient. In contrast, the gross EOTS was slower than the net EOTS at the level (7.49 ± 0.32 vs. 7.63 ± 0.36 km·h-1, P = 0.003) and downhill gradients (7.78 ± 0.33 vs. 8.01 ± 0.41 km·h-1, P < 0.001), but not at the uphill gradient (7.55 ± 0.37 vs. 7.63 ± 0.51 km·h-1, P = 0.080). Note that those percent differences were less than 2.9%. Given these results, a subtraction of the standing oxygen cost should be carefully considered depending on the purpose of each study. 相似文献