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31.
Alexander Steinkasserer Tania Jones Denise Sheer Karl Koettnitz Joachim Hauber Dorian Bevec 《Genomics》1995,25(3)
The eukaryotic initiation factor 5A (eIF-5A) has been identified as an essential cofactor for the HIV-1 trans-activator protein Rev. Rev plays a key role in the complex regulation of HIV-1 gene expression and thereby in the generation of infectious virus particles. Expression of eIF-5A is vital for Rev function, and inhibition of this interaction leads to a block of the viral replication cycle. In humans, four different eIF-5A genes have been identified. One codes for the eIF-5A protein and the other three are pseudogenes. Using a panel of somatic rodent—human cell hybrids in combination with fluorescence in situ hybridization analysis, we show that the four genes map to threedifferent chromosomes. The coding eIF-5A gene (EIF5A) maps to 17p12–p13, and the three pseudogenes EIF5AP1, EIF5AP2, and EIF5AP3 map to 10q23.3, 17q25, and 19q13.2, respectively. This is the first localization report for a eukaryotic cofactor for a regulatory HIV-1 protein. 相似文献
32.
Determinants of the high-methionine trait in wild and exotic germplasm may have escaped selection during early cultivation of maize 总被引:3,自引:1,他引:2
Sanjay Swarup Marja C.P. Timmermans Sumita Chaudhuri Joachim Messing 《The Plant journal : for cell and molecular biology》1995,8(3):359-368
The 18 kDa high-methionine δ-class zein gene from maize has been cloned, and its regulation, structure, and map position studied. These studies have shown that (i) zein genes may also contain tryptophan and lysine codons, (ii) the 18 kDa and the related 10 kDa zein gene are coordinately regulated, but their products accumulate to different levels in a genotype-dependent manner, (iii) the duplication of δ-zein genes probably involved unequal crossing over, (iv) no copy correction in either direction has occurred from teosinte to modern corn, and (v) the duplication of of the 18 kDa zein gene probably occurred before the tetraploidization of a progenitor chromosome. The work shows that important nutritional quality determinants like the high-methionine seed proteins are abundant in several exotic and wild corn varieties and low in most of the inbreds screened. The lack of a selectable phenotype for such quality traits during initial domestication and breeding of corn would have eliminated cis and trans regulatory determinants from the germplasm used in modern corn breeding. Examples of the high-methionine δ-class zeins shown here may be generally applicable in explaining the low nutritional quality of most present-day corn grown. 相似文献
33.
Using an immunoblotting technique and goat antihuman C4, we observed five distinct electrophoretic variants of C4 in a panel of 60 random dogs. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of immunoprecipitated C4 showed that dog C4 is composed of three polypeptide subunit chains (, , and ) and that structural variability occurs within the - and -chain regions. Two distinct molecular weight forms of both the C4- (
A and
B) and C4-(
A and
B) chain were detected. The variant forms of C4 and C4 were found in association with particular C4 allotypes. 相似文献
34.
InEscherichia coli, NADP+-specific isocitrate dehydrogenase (EC 1.1.1.42) may undergo a phosphorylation catalyzed by a cAMP-independent protein kinase, with a concomitant decrease in catalytic activity. In this report, we describe the purification and amino acid sequence of a32P-labeled peptide obtained from in vivo32P-labeled isocitrate dehydrogenase. The32P-labeled peptide was isolated from a tryptic digest and found to contain seven amino acids, including a single serine residue. Following automated Edman degradation and reversephase high-pressure liquid chromatography of the phenylthiohydantoin-amino acids, the sequence of this peptide was established to be-Ser(P)-Leu-Asn-Val-Ala-Leu-Arg. 相似文献
35.
Can Nocodazole,an Inhibitor of Microtubule Formation,Be Used to Synchronize Mammalian Cells? 总被引:6,自引:0,他引:6
Abstract Nocodazole, a temporary inhibitor of microtubule formation, has been used to partly synchronize Ehrlich ascites tumour cells growing in suspension. the gradual entry of cells into mitosis and into the next cell cycle without division during drug treatment has been studied by flow cytometric determination of mitotic cells, analysing red and green fluorescence after low pH treatment and acridine orange staining. Determination of the mitotic index (MI) by this method has been combined with DNA distribution analysis to measure cell-cycle phase durations in asynchronous populations growing in the presence of the drug. With synchronized cells, it was shown that in the concentration range 0.4–4.0 μg/l, cells could only be arrested in mitosis for about 7 hr and at 0.04 μg/ml, for about 5 hr. After these time intervals, the DNA content in nocodazole-blocked cells was found to be increased, and, in parallel, the ratio of red and green fluorescence was found to have changed, showing entry of cells into a next cell cycle without division (polyploidization). It was therefore only possible to partially synchronize an asynchronous population by nocodazole. However, a presynchronized population, e.g. selected G1 cells or metabolically blocked G1/S cells, were readily and without harmful effect resynchronized in M phase by a short treatment (0.4 μg/ml, 3–4 hr) with nocodazole; after removal of the drug, cells divided and progressed in a highly synchronized fashion through the next cell cycle. 相似文献
36.
Summary The ultrastructure of the thread-like hairs (sensilla) on the tibia of the front leg ofAcheta domesticus (Gryllidae) Saltatoria was examined by serial sectioning. The presence of a tubular body indicates that these sensilla are mechanosensitive; electrophysiological measurements also confirmed this. The opposing forces on the articulating apparatus of single hairs and the sensitivity of the single receptor cell were measured after deflection of the hair in different directions. The articulating apparatus is characterized by three cuticular elements: a joint membrane, suspension fibers, and a socket septum. These elements form the basis for a structural bilateral symmetry along whose plane of symmetry the direction line of both the minimum receptor sensitivity and the minimum opposing forces lie. The tubular body embedded in the tip of the socket septum is attached to the base of the hair shaft. The hair provides the leverage for displacing the tubular body and the socket septum limits the extent to which it may be laterally displaced.These investigations have been supported by the Deutsche Forschungsgemeinschaft 相似文献
37.
A photoreactive analog of aminopterin, 2′-azidoaminopterin (VI), was synthesized and evaluated as a potential inhibitor and photoaffinity label of folate-utilizing enzymes. The compound was tightly bound to dihydrofolate reductase (DHFR) from escherichia coli (MB 1428) with K1 equal to 3 × 10?11M and to the enzyme from mouse (S-180) cells with K1 approximately equal to 2 × 10?10M. Dissociation constants measured by equilibrium dialysis using radioactive 2′-azidoaminopterin gave a value of KD = 3.2 × 10?9M for the bacterial enzyme. The presence of NADPH enhanced the affinity by more than an order of magnitude. Azidoaminopterin is also an inhibitor of thymidylate synthetase from Lactobacillus casei, competitive with methylene-tetrahydrofolate (Ki 7 × 10?7M). Photolysis of the radioactive inhibitor in complex with DHFR from E. coli led to approximately 3% covalent incorporation of label into protein. The greater part of this attachment was nonspecific as shown by the lack of protection in the presence of methotrexate. Thymidylate synthetase from L. casei was not significantly inactivated upon photolysis in the presence of the inhibitor and deoxyuridylate. Model studies showed that photoreaction of the inhibitor led to covalent linkages with thiol, lysyl amino groups, and the hydroxyl groups of alcohols. Azidoaminopterin may be useful in labeling other enzymes of folate metabolism, although a minor photoproduct reacts nonspecifically with many proteins. The antifolate can be photoconjugated to polylysine as well as to proteins. The polylysine conjugates inhibit DHFR. Difference spectrum analysis of the photoproducts from the irradiation of the DHFR I complex indicates that water reacts efficiently with the enzyme-bound nitrene and must therefore have access to at least part of the bound p-aminobenzoyl group. This analysis suggests that azide analogs of protein ligands may be useful as reporter groups in probing the hydrophobicity of binding sites. 相似文献
38.
39.
A new approach for the reaction of Sepharose with cyanogen bromide is described, using triethylamine as a “cyano-transfer” reagent. An optimized procedure for activation at neutral pH was developed. This procedure requires only about 5% of the usual amount of cyanogen bromide. Activated resins are free of imidocarbonates and carbamates, containing only active cyanate esters. Extremely high coupling capacities (75 μmol ligand/g wet Sepharose 4B) can be obtained using this method. 相似文献
40.