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Tunicamycin, an antibiotic that inhibits protein glycosylation, elicited a rapid depletion of insulin binding activity at the surface of 3T3-L1 adipocytes. Disappearance of insulin receptors occurred more rapidly in the presence of tunicamycin than when protein synthesis was inhibited by cycloheximide and was accompanied by a diminution in sensitivity of the adipocytes to the acute effects of insulin and anti-insulin receptor antibody on hexose uptake and metabolism. 相似文献
14.
Summary The two statocysts of the veliger larva of Rostanga pulchra are positioned within the base of the foot. They are spherical, fluid-filled capsule that contain a large, calcareous statolith and several smaller concretions. The epithelium of the statocyst is composed of 10 ciliated sensory cells (hair cells) and 11 accessory cells. The latter group stains darkly and includes 2 microvillous cells, 7 supporting cells, and 2 glial cells. The hair cells stain lightly and each gives rise to an axon; two types can be distinguished. The first type, in which a minimum of 3 cilia are randomly positioned on the apical cell membrane, is restricted to the upper portion of the statocyst. The second type, in which 9 to 11 cilia are arranged in a slightly curved row, is found exclusively around the base of the statocyst. Each statocyst is connected dorso-laterally to the ipsilateral cerebral ganglion by a short static nerve, formed by axons arising from the hair cells. Ganglionic neurons synapse with these axons as the static nerve enters the cerebral ganglion. The lumen of the statocyst is continuous with a blind constricted canal located beneath the static nerve.A diagram showing the structure of the statocyst and its association with the nervous system is presented. Possible functions of the statocyst in relation to larval behavior are discussed. 相似文献
15.
Summary A genetic locus has been identified which controls the basal synthesis of ppGpp in growing E. coli. Cells carrying a recessive allele of the relX gene have a very low concentration of ppGpp during balanced growth, and fail to accumulate ppGpp in response to carbon/energy source downshift. Moreover, the recessive relX allele renders the cells unable to grow at 42° C and, when coupled with relA, makes the cells sensitive to the presence of leucine in minimal medium. RelX is cotransduced with fuc and relA and located at approximately 59.4 min on the E. coli genetic map. 相似文献
16.
The structural gene for pyruvate kinase from Bacillus stearothermophilus has been cloned in Escherichia coli and sequenced. The open reading frame from the ATG start codon to the TAG stop codon is 1482 base-pairs and encodes a peptide of relative molecular mass 52,967. In the expression vector pKK223-3, containing the synthetic tac promoter, the gene is overexpressed in E. coli cells to an estimated level of 30% total soluble cell protein. A purification procedure for the overexpressed protein has been established. The construction and characterization of a pair of mutant proteins has given insight into the structural basis of allosteric regulation in the tetrameric enzyme. Substituting tryptophan for tyrosine at position 466 (mutant Trp466-->Tyr) resulted in an activated form of the enzyme, having a reduced K1/2 for the substrate phosphoenolpyruvate. We propose that the characteristics of this mutant might be the result of bulk removal releasing steric inhibition to the formation of an interdomain salt bridge between Asp356 and Arg444. The regulatory behaviour of the double mutant produced by making the additional substitution aspartate for glutamate at position 356 (Trp466-->Tyr/Asp356-->Glu) corroborates this. The position of the salt bridge is such that it might be pivotal to the conformation of a pocket that is proposed to open up when the active R-conformation is adopted. We suggest that the mechanism of activation of B. stearothermophilus pyruvate kinase by ribose-5-phosphate might hinge on an interaction with, or indirectly through, residue Trp466, removing it from the vicinity of the potential salt bridge between Asp356 and Arg444 and thus effecting a closing together of the protein structure concomitant with an opening up of the pocket region. 相似文献
17.
Cymbidium mosaic virus (CyMV) is the most prevalent virus infecting orchids. Here, we report the isolation of partial cDNA clones encoding the genomic RNA of CyMV. Like most of the polyadenylated monopartite positive-strand RNA viruses, the open reading frame (ORF) coding for the viral coat protein (CP) is located at the 3 end. The ORF predicts a polypeptide chain of 220 amino acids with a molecular weight of 23 600. Sequence comparison of this ORF to the CP sequences of potato virus X(PVX) and white clover mosaic virus (WCIMV) revealed a strong amino acid homology in the mid-portion of the CP, but the overall homology was low. The CyMV CP gene was placed downstream of a cauliflower mosaic virus 35S promoter and the chimaeric gene was transferred into Nicotiana benthamiana. Transgenic plants expressing the CyMV CP were protected against CyMV infection. 相似文献
18.
The construction of cosmid libraries of eukaryotic DNA using the Homer series of vectors 总被引:11,自引:3,他引:8
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We have constructed and characterised a series of approved, disabled cosmid vectors which we call Homer cosmids and have examined the optimal conditions for the construction of libraries of eukaryotic DNA segments using these vectors. Analysis of these libraries shows that most of the sequences we have tested for are present at the expected frequency and that the libraries can be stably propagated. We have also directly tested the stability of cosmid clones carrying tandemly repeated inserts. This work shows that it should be possible to clone most eukaryotic genes using cosmid vectors and that such cloning systems have considerable advantages over those more commonly used. 相似文献
19.
E W Kraegen R Whiteside D Bell Y O Chia L Lazarus 《Hormone and metabolic research. Supplement series》1979,(8):38-42
A closed-loop glucose controlled insulin infusion system was developed, consisting of elements for continuous blood glucose analysis, a computer control system, and infusion systems. Improvements include decreased size, cost reduction and better performance. The algorithm used was a piecewise linear representation of the sigmoidal curve commonly employed. The apparatus has been applied to simulation of the healthy beta cell and glucose clamp studies. 相似文献
20.
W K Chia 《Developmental biology》1975,44(2):239-252
The P-4 variant of Dictyostelium discoideum (DdH) was found to produce a great excess of stalk cells compared to the wild type DdH. If the vegetative cells of P-4 were repeatedly washed, the variant changed back to the wild type phenotype, and if cyclic-AMP was added to the washed P-4 cells, the variant character was restored. Furthermore, if the concentration of added cyclic-AMP was increased, it was possible to induce 100% stalk cells in P-4. Phosphodiesterase would cause the variant to change to the wild type, while 5-AMP and cyclic-nucleotides other than cyclic-AMP have no effect at all. Therefore it was concluded that cyclic-AMP plays a key role in stalk cell differentiation.A comparison between wild type DdH and the variant P-4 showed that DdH is ten times less sensitive to cyclic-AMP induction. They both produce the same amount of cyclic-AMP and extracellular phosphodiesterase, but the specific activity of P-4 cell-bound phosphodiesterase during development is significantly less than that in the DdH. One hypothesis that accounts for the P-4-DdH difference is that because of the lack of cell-bound phosphodiesterase, more cyclic-AMP enters the variant cells and hence more stalk cell differentiation. 相似文献