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41.
Mutational analysis of Saccharomyces cerevisiae U4 small nuclear RNA identifies functionally important domains. 总被引:1,自引:0,他引:1 下载免费PDF全文
U4 small nuclear RNA (snRNA) is essential for pre-mRNA splicing, although its role is not yet clear. On the basis of a model structure (C. Guthrie and B. Patterson, Annu. Rev. Genet. 22:387-419, 1988), the molecule can be thought of as having six domains: stem II, 5' stem-loop, stem I, central region, 3' stem-loop, and 3'-terminal region. We have carried out extensive mutagenesis of the yeast U4 snRNA gene (SNR14) and have obtained information on the effect of mutations at 105 of its 160 nucleotides. Fifteen critical residues in the U4 snRNA have been identified in four domains: stem II, the 5' stem-loop, stem I, and the 3'-terminal region. These domains have been shown previously to be insensitive to oligonucleotide-directed RNase H cleavage (Y. Xu, S. Petersen-Bjørn, and J. D. Friesen, Mol. Cell. Biol. 10:1217-1225, 1990), suggesting that they are involved in intra- or intermolecular interactions. Stem II, a region that base pairs with U6 snRNA, is the most sensitive to mutation of all U4 snRNA domains. In contrast, stem I is surprisingly insensitive to mutational change, which brings into question its role in base pairing with U6 snRNA. All mutations in the putative Sm site of U4 snRNA yield a lethal or conditional-lethal phenotype, indicating that this region is important functionally. Only two nucleotides in the 5' stem-loop are sensitive to mutation; most of this domain can tolerate point mutations or small deletions. The 3' stem-loop, while essential, is very tolerant of change. A large portion of the central domain can be removed or expanded with only minor effects on phenotype, suggesting that it has little function of its own. Analysis of conditional mutations in stem II and stem I indicates that although these single-base changes do not have a dramatic effect on U4 snRNA stability, they are defective in RNA splicing in vivo and in vitro, as well as in spliceosome assembly. These results are discussed in the context of current knowledge of the interactions involving U4 snRNA. 相似文献
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新疆10种沙生植物旱生结构的解剖学研究 总被引:17,自引:1,他引:16
新疆10种沙生植物的形态解剖研究表明,它们为适应沙生环境形态结构发生变化。叶器官的形态呈三种类型:叶片退化成膜质或鳞片状,而由同化枝执行光合功能;叶片上下都具栅栏组织,表皮角质膜厚,表皮毛发达,气孔下陷,输导组织和机械组织都发达;叶片肉质化,叶肉组织不分化,贮水组织发达而输导组织不发达。轴器官中厚壁组织发达,围绕维管组织,维管组织内部也有发达的厚壁组织。根中普遍具有周皮,一些植物存在异常的维管组织,部分植物还具有粘液细胞或结晶。沙生植物形成各种旱生结构,以不同的方式适应沙生环境。 相似文献
45.
Bernadine Hu John W. McDonald Michael V. Johnston† Faye S. Silverstein 《Journal of neurochemistry》1991,56(3):933-937
In immature rodent brain, the glutamate receptor agonist N-methyl-D-aspartate (NMDA) is a potent neurotoxin. In postnatal day (PND)-7 rats, intrastriatal injection of 25 nmol of NMDA results in extensive ipsilateral forebrain injury. In this study, we examined alterations in high-affinity [3H]glutamate uptake (HAGU) in NMDA-lesioned striatum. HAGU was assayed in synaptosomes, prepared from lesioned striatum, the corresponding contralateral striatum, or unlesioned controls. Twenty-four hours after NMDA injection (25 nmol), HAGU declined 44 +/- 8% in lesioned tissue, compared with the contralateral striatum (mean +/- SEM, n = 6 assays, p less than 0.006, paired t test). Doses of 5-25 nmol of NMDA resulted in increasing suppression of HAGU (5 nmol, n = 3; 12.5 nmol, n = 3; and 25 nmol, n = 5 assays; p less than 0.01, regression analysis). The temporal evolution of HAGU suppression was biphasic. There was an early transient suppression of HAGU (-28 +/- 4% at 1 h; p less than 0.03, analysis of variance, comparing changes at 0.5, 1, 2, and 3 h after lesioning); 1 or 5 days postinjury there was sustained loss of HAGU (at 5 days, -56 +/- 11%, n = 3, p less than 0.03, paired t test, lesioned versus contralateral striata).(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
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本文报告尖吻蝮咬伤并心脏受累20例。经中西医结合治愈19例(95%),死亡1例(5%),并对其发病机理及治疗进行了讨论。 相似文献
48.
Shung-Tai Ho Jhi-Joung Wang Weber Ho
Oliver Yoa-Pu Hu
《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1991,570(2):339-350A rapid, sensitive, precise and accurate high-performance liquid chromatographic assay with fluorescence detection was developed for the determination of buprenorphine in human, rabbit, pig and dog plasma. It is comprised of only a one-step extraction procedure with hexane—isoamyl alcohol at pH 9.25 and reversed-phase chromatography on a μPorasil column. The recoveries of buprenorphine and nalbuphine (internal standard) were greater than 90%. Calibration graphs were linear over the concentration range 3–300 ng/ml with a coefficient of variation, both within-day and between-day, of less than 9% at any level. The limit of detection was 1.0 ng/ml of plasma based on a signal-to-noise ratio of 3. Eight other clinically used narcotics were investigated to check for potential interferences and their analytical conditions. The possible decomposed compounds of buprenorphine were also checked for the specificity of this assay. The method has been succesfully applied to the stability and pharmacokinetic studies of buprenorphine. Buprenorphine in plasma did not decompose significantly at −20°C for four weeks. Pharmacokinetic application in six rabbits and a surgical patient revealed that buprenorphine followed a linear three-compartment model with two distribution phases. The two distribution and elimination half-lives and the clearance of buprenorphine were 1.32, 24.8 and 230 min and 224 ml/min in human plasma, and 0.94, 12.5 and 232 min and 30 ml/min in rabbit plasma. 相似文献
49.
B Halliwell M L Hu S Louie T R Duvall B K Tarkington P Motchnik C E Cross 《FEBS letters》1992,313(1):62-66
Nitrogen dioxide (NO2.) is often present in inhaled air and may be generated in vivo from nitric oxide. Exposure of human blood plasma to NO2. caused rapid losses of ascorbic acid, uric acid and protein thiol groups, as well as lipid peroxidation and depletions of alpha-tocopherol, bilirubin and ubiquinol-10. No increase in protein carbonyls was detected. Supplementation of plasma with ascorbate decreased the rates of lipid peroxidation, alpha-tocopherol depletion and loss of uric acid. Uric acid supplementation decreased rates of lipid peroxidation but not the loss of alpha-tocopherol. We conclude that ascorbic acid, protein -SH groups, uric acid and alpha-tocopherol may be important agents protecting against NO2. in vivo. If these antioxidants are depleted, peroxidation of lipids occurs and might contribute to the toxicity of NO2.. 相似文献
50.
The intraperitoneal injection of anaesthetic agents is a simple and convenient method of anaesthetizing rats. However, all of the anaesthetic combinations in current use which are administered by intraperitoneal injection produce prolonged sedation, and full recovery of consciousness may take several hours. Fentanyl, a mu agonist opioid, and medetomidine, an alpha 2-adrenoceptor agonist were mixed and administered as a single intraperitoneal injection. Combinations of 300 micrograms/300 micrograms/kg and 300 micrograms/200 micrograms/kg of fentanyl/medetomidine were shown to produce surgical anaesthesia in the rat. This anaesthetic regimen produced significant respiratory depression (P less than 0.01) and animals did not regain their righting reflex until 193 +/- 21 min (mean +/- 1 SD) after injection. Administration by intraperitoneal injection of atipamezole, a specific alpha 2-adrenoceptor antagonist (1 mg/kg) mixed with a mu antagonist/k agonist opioid (nalbuphine, 2 mg/kg or butorphanol 0.4 mg/kg), resulted in a rapid (less than 8 min) reversal of anaesthesia and the associated respiratory depression, and apparent full recovery of consciousness. 相似文献