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81.
82.
Scott Pownall Christine A. Kozak Keith Schappert Mohan Sarkar Eric Hull Harry Schachter Jamey D. Marth 《Genomics》1992,12(4)
The biosynthesis of protein-bound complex N-glycans in mammals requires a series of covalent modifications governed by a large number of specific glycosyltransferases and glycosidases. The addition of oligosaccharide to an asparagine residue on a nascent polypeptide chain begins in the endoplasmic reticulum. Oligosaccharide processing continues in the Golgi apparatus to produce a diversity of glycan structures. UDP-N-acetylglucosamine:α-3-
-mannoside β-1,2-N-acetylglucosaminyltransferase I (EC 2.4.1.101; GlcNAc-TI) is a key enzyme in the process because it is essential for the conversion of high-mannose N-glycans to complex and hybrid N-glycans. We have isolated the mouse gene encoding GlcNAc-TI (Mgat-1) from a genomic DNA library. The mouse sequence is highly conserved with respect to the human and rabbit homologs and exists as a single protein-encoding exon. Mgat-1 was mapped to mouse Chromosome 11, closely linked to the gene encoding interleukin-3 by the analysis of multilocus interspecies backcrosses. RNA analyses of Mgat-1 expression levels revealed significant variation among normal tissues and cells. 相似文献
83.
84.
Neurons require a large amount of intracellular transport. Cytoplasmic polypeptides and membrane-bounded organelles move from
the perikaryon, down the length of the axon, and to the synaptic terminals. This movement occurs at distinct rates and is
termed axonal transport. Axonal transport is divided into the slow transport of cytoplasmic proteins including glycolytic
enzymes and cytoskeletal structures and the fast transport of membrane-bounded organelles along linear arrays of microtubules.
The polypeptide compositions of the rate classes of axonal transport have been well characterized, but the underlying molecular
mechanisms of this movement are less clear. Progress has been particularly slow toward understanding force-generation in slow
transport, but recent developments have provided insight into the molecular motors involved in fast axonal transport. Recent
advances in the cellular and molecular biology of one fast axonal transport motor, kinesin, have provided a clearer understanding
of organelle movement along microtubules. The availability of cellular and molecular probes for kinesin and other putative
axonal transport motors have led to a reevaluation of our understanding of intracellular motility. 相似文献
85.
D Scott S M Galloway R R Marshall M Ishidate D Brusick J Ashby B C Myhr 《Mutation research》1991,257(2):147-205
86.
J M Egan C M Asplin M A Drumheller J R Kerrigan J Scott P M Martha W S Evans 《Proceedings of the Society for Experimental Biology and Medicine. Society for Experimental Biology and Medicine (New York, N.Y.)》1991,196(2):203-209
To investigate the effect of glyburide on insulin secretion by individual beta cells from normal rats, we employed a reverse hemolytic plaque assay. Pancreata were harvested from female Wistar-Furth rats, the pancreatic islets isolated, and the latter dispersed into single cells. These cells were mixed with protein A-coated ox erythrocytes, the mixture was placed in a Cunningham chamber in the presence of insulin antiserum, and the cells were exposed to the various test substances. Having developed hemolytic plaques around the insulin-secreting cells with complement, the percentage of plaque-forming cells was determined and the plaque areas (reflecting the amount of insulin secreted) were quantitated. For the purpose of validation, we demonstrated that (i) plaque-forming (but not nonplaque-forming) cells could be identified as insulin secreting by an independent immunofluorescent technique, (ii), plaques did not form if insulin antiserum was deleted from the preparation, (iii) plaques failed to develop if insulin antiserum was preabsorbed with insulin, and (iv) incubation with non-protein A-coated RBC or omission of complement resulted in no plaque formation. In addition, both the percentage of plaque-forming cells and the mean plaque are increased upon exposure to glucose (0.75-20 mM) in a concentration-dependent manner at 5- and 60-min incubation times. Moreover, somatostatin suppressed the percentage of plaque-forming cells and diminished the mean plaque area of cells which continued to secrete insulin in response to glucose. Exposure of cells to 100 nM glyburide in the presence of 5 mM or 20 mM glucose had no effect on the percentage of plaque-forming cells present at 5 min or 60 min. Similarly, glyburide did not alter mean plaque area at 5 or 60 min when cells were co-incubated with 5 mM glucose. However, mean plaque area was markedly enhanced at 5 and 60 min in response to glyburide and 20 mM glucose. These results demonstrate that glyburide (i) does appear to enhance insulin secretion by an effect directly on the pancreatic beta cell; (ii) does not act by recruiting previously noninsulin-secreting cells into a secretory pool; (iii) does not potentiate the effect of glucose, at fed concentrations, on insulin secretion by individual cells; but (iv) does augment insulin secretion by beta cells stimulated with supraphysiologic concentrations of glucose. 相似文献
87.
A micropropagation system was developed to test concepts for automation and microenvironment alteration. Amelanchier x grandiflora Rehd. Princess Diana (serviceberry) shoot cultures were grown in seven-liter polycarbonate containers. Through computer control, the apparatus intermittently applied culture medium to the plant material according to a selected schedule. Shoot growth in the programmable system was compared with four micropropagation treatments: gelled and liquid medium in baby food jars and gelled and non-cycling liquid medium in a seven-liter vessel. Plants cultured in continuous contact with liquid medium became increasingly vitrified. Significantly greater shoot number, shoot length, shoot weight, and culture weight occurred in the programmable system than in jars with gelled medium. The combination of liquid medium, 7-liter vessel, and intermittent contact with medium caused a significantly higher proliferation rate than any combination of jar/vessel and gelled/liquid medium tested. 相似文献
88.
Traditionally, the major biotic determinants of animal community structure were assumed to be competition and predation. Recent theoretical, experimental and field studies indicate that parasitism is also important. The spectrum of effects that parasites have on host individuals is as broad as the range of parasite-host interactions. This review considers evidence for direct effects of parasites on fecundity and survival that influence host demography, and for indirect effects on host physiology and behavior that interface with competition and predation. 相似文献
89.
Construction and expression of nonsense suppressor tRNAs which function in plant cells 总被引:3,自引:0,他引:3
Scott Franklin Tsai Yun Lin William R. Folk 《The Plant journal : for cell and molecular biology》1992,2(4):583-588
An Arabidopsis thaliana L. DNA containing the tRNA(TrpUGG) gene was isolated and altered to encode the amber suppressor tRNA(TrpUAG) or the ochre suppressor tRNA(TrpUAA). These DNAs were electroporated into carrot protoplasts and tRNA expression was demonstrated by the translational suppression of amber and ochre nonsense mutations in the chloramphenicol acetyltransferase (CAT) reporter gene. DNAs encoding tRNA(TrpUAG) and tRNA(TrpUAA) nonsense suppressor tRNAs caused suppression of their cognate nonsense codons in CAT mRNAs, with the tRNA(TrpUAG) gene exhibiting the greater suppression under optimal conditions for expression of CAT. The development of these translational suppressors which function in plant cells facilitates the study of plant tRNA gene expression and will make possible the manipulation of plant protein structure and function. 相似文献
90.
Mark A. Wolters Mary E. Bodnar Mary D. Strem Scott E. Bingham 《Applied microbiology and biotechnology》1991,35(1):56-59
Summary In order to deregulate arginine biosynthesis in Synechococcus sp. PCC7942, d-arginine-resistant cell lines were selected following ethyl methanesulfonate mutagenesis of wild-type (WT) cells. Three of these arginine-producing mutant (APM) cell lines, APM1, APM31 and APM40, were putative regulatory mutants based upon secretion of l-arginine into their growth medium. HPLC of lyophilized post-harvest supernatants of APM 31 and 40 resolved two predominant amino acids, arginine and citrulline. In-vitro activity of N-acetylglutamate kinase (NAGK), the proposed regulatory enzyme of the arginine pathway, was about 100-fold less sensitive to l-arginine inhibition in extracts from APM 31 and 40 than the enzyme in WT extracts. The enzyme from APM 1 was 20-fold less sensitive to l-arginine inhibition than WT. The most likely site of mutation in each of the APM cell lines is in the gene for NAGK, rendering the enzymes insensitive to l-arginine feedback control. These strains can be utilized for the phototrophic production of arginine.
Offprint requests to: S. E. Bingham 相似文献