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21.
The nucleotide sequence data reported in this paper have been submitted to the GenBank nucleotide sequence database and have been assigned the accession numbers U03104 and L22338. 相似文献
22.
Summary Three techniques for measuring plasmid stability in yeasts are described and evaluated. The yeast used was aKluyveromyces lactis strain which was transformed with a plasmid, pCR1, to enable production of heterologous α-amylase. The techniques were based
on plate counts on a selective antibiotic-containing medium and a non-selective medium, and on clearing zones on starch-supplemented
plates for α-amylase detection. The plate ratio and clearing zones methods gave comparable results while the transfer colony
method estimated much lower plasmid stabilities. 相似文献
23.
Robert L. Deresiewicz Paula R. Austin Carolyn J. Hovde 《Molecular & general genetics : MGG》1993,241(3-4):467-473
Shiga-like toxin I (SLT-I), the potent cytotoxin produced by certain pathogenic strains of Escherichia coli, is a member of a burgeoning family of ribosome-inactivating proteins (RIPS), which share common structural and mechanistic features. The prototype of the group is the plant toxin ricin. Recently we proposed a structural model for the Slt-IA active site, based in part on the known geometry of the enzymatic subunit of the ricin toxin. The model places three aromatic residues within the putative Slt-IA active site cleft: tyrosine 77, tyrosine 114, and tryptophan 203. Here we present biochemical and biophysical data regarding, the phenotypes of conservative point mutants of Slt-IA in which tyrosine 114 is altered. We used oligonucleotide-directed mutagenesis to replace tyrosine 114 with either phenylalanine (Y114F) or serine (Y114S). Periplasmic extracts of E. coli containing wild-type or mutant Slt-IA were tested for their ability to inhibit protein synthesis in vitro. Relative to wild-type, the activity of mutant Y1 14F was attenuated about 30-fold, while the mutant Y114S was attenuated about 500 to 1000-fold. In order to address the possibility that differential activation of the mutants rather than local effects at the active site might account for their diminished activity, we engineered the same mutations into a truncated slt-IA cassette that directs expression of a product corresponding to the activated A1 form of Slt-IA (wild-type-). The same general relationships held: relative to wild type-, Y114F- was attenuated about 7-fold, and Y114S- about 300-fold. Tryptic digestion profiles of the mutant proteins were similar to those of the corresponding wild-type, indicating that the amino acid substitutions had not caused major alterations in conformation. We conclude that Y114 plays a significant role in the activity of Slt-IA, one which is quantitatively similar to that of Y77, and one which is predicated on the presence of both its weakly acidic phenolic hydroxyl and its aromatic ring. 相似文献
24.
Carolyn Russell Audrey Jarvis Pak-Lam Yu John Mawson 《Applied microbiology and biotechnology》1993,40(2-3):306-308
The plasmid pCR1 has been constructed to express a wheat -amylase enzyme in Kluyveromyces lactis strains. The contruct is based on the vector pCXJ-kan1, which has been derived from pDK1, a native plasmid of K. lactis var. drosophilarum containing the essential regions for plasmid replication and stability. Contruct pCR1 produces an -amylase by DNA isolated from a wheat cDNA clone and is controlled by a Saccharomyces cerevisia PGK promoter.
Correspondence to: C. Russell 相似文献
25.
Laurence M. Demers Allan Lipton Harold A. Harvey Kathleen B. Kambic Howard Grossberg Carolyn Brady Richard J. Santen 《The Journal of steroid biochemistry and molecular biology》1993,44(4-6):687-691
The pharmacologic inhibition of aromatase activity has been the focus of clinical trials in patients with advanced stage breast cancer. Recent developments with imidazole compounds that inhibit aromatase activity suggest their clinical use as potent inhibitors of estrogen biosynthesis in postmenopausal breast cancer patients. In this Phase I, open-label, dose-range finding study, we examined the inhibitory potency of CGS 20267 on blood and urine levels of estradiol, estrone and estrone sulfate in 8 patients with metastatic breast cancer. Studies included evaluation of adrenal and thyroid function to look for evidence of general hydroxylase inhibition at dose levels effective for aromatase blockade. Patients were administered CGS 20267 at doses of 0.1 and 0.25 mg, once a day in ascending doses over a 12-week period. Preliminary data reveal that CGS 20267 elicits a striking suppression in plasma estradiol, estrone and estrone sulphate which was observed in some patients as quickly as within 24 h of the first dose. Estrogen suppression of over 90% was achieved within 2 weeks of therapy. No alterations in either baseline or ACTH (cortrosyn) stimulated cortisol and aldosterone levels were observed through the 12 weeks of therapy. In addition, 24 h urine sodium and potassium values were not appreciably altered during therapy. We conclude that CGS 20267 is a potent, specific inhibitor of estrogen biosynthesis in postmenopausal patients with metastatic breast cancer and effectively reduces blood and urine estrogens to undetectable levels. 相似文献
26.
Glycans of the early human yolk sac 总被引:2,自引:0,他引:2
Summary The pattern of glycan distribution in the early human yolk sac has been investigated using a panel of lectins. Two 6-week
and one 8-week human yolk sacs, and one 8-week fetal liver from live, ectopic pregnancies were fixed and embedded in epoxy
resin. Lectin histochemistry was carried out on sections of these tissues using 23 biotinylated lectins and an avidin-biotin
peroxidase revealing system. Mesothelial surfaces expressed most subsets of N-glycans (other than high mannose types),N-acetyl-lactosamine, sialic acid, andα1,6-N-acetylgalactosamine. Endodermal surface and lateral membranes resembled those of mesothelium, but showed a preponderance
ofα2,6-sialyl residues. Most intracellular granules contained N-glycan. There was a marked heterogeneity of granules in the endodermal
cells, with different subsets varying in both staining and positional characteristics. The mesenchymal matrix bound most of
the lectins used in the study, and expressed fucosyl residues which were also detected in the endothelium. Fetal liver parenchyma
showed very similar staining patterns to those seen in the endoderm except for the distribution ofN-acetylglucosamine, which was sparse. Despite some common features, each germ cell layer had a distinct ‘glycotype’, with
some saccharides showing extreme topographical restriction. 相似文献
27.
The aspartate aminotransferase gene family of Arabidopsis encodes isoenzymes localized to three distinct subcellular compartments 总被引:5,自引:1,他引:4
Carolyn J. Schultz Gloria M. Coruzzi 《The Plant journal : for cell and molecular biology》1995,7(1):61-75
Here, a complete study is described of all the genes and isoenzymes for aspartate aminotransferase (AspAT) present in Arabidopsis thaliana . Four classes of cDNAs representing four distinct AspAT genes ( ASP1—ASP4 ) have been cloned from Arabidopsis . Sequence analysis of the cDNAs suggests that the encoded proteins are targeted to different subcellular compartments. ASP1 encodes a mitochondrial form of AspAT, ASP3 encodes a chloroplastic/plastidic form of AspAT, whereas ASP2 and ASP4 each encode cytosolic forms of AspAT. Three distinct AspAT holoenzymes (AAT1—AAT3) were resolved by activity gel analysis. Organelle isolation reveals that AAT1 is mitochondrial-localized, AAT3 is plastid-localized, and AAT2 is cytosolic. Gene-specific Northern analysis reveals that each Asp mRNA accumulates differentially with respect to organ-type. However, the individual Asp mRNAs show no dramatic fluctuations in response to environmental stimuli such as light. Southern analysis reveals that four distinct nuclear genes probably represent the entire AspAT gene family in Arabidopsis . These molecular studies shed light on the subcellular synthesis of aspartate in Arabidopsis and suggest that some of the AspAT isoenzymes may play overlapping roles in plant nitrogen metabolism. 相似文献
28.
G. Mauff K. Bender Carolyn M. Giles S. Goldmann W. Opferkuch Barbara Wachauf 《Human genetics》1984,65(4):362-372
Summary Ten families with 82 members were investigated for C4A- and B polymorphism in a blind trial. Phenotyping was done on neuraminidase treated sera by immunofixation and simulataneously by hemolytic overlay electrophoresis. In addition Rg, Ch, BF, C2, HLA-A, B, C, DR, and GLO were determined. After decoding the samples the reliability of blind typing was found to be 84.4% according to segregation patters. Inconsistencies occurred mostly when A 4, A 2, or A 92 were present. The detection of silent A*Q0 and B*Q0 alleles was more critical than that of difficult allotypes. The quantitation of the C4A/B ratio by densitometry of stained gels or by conventional immunochemical measurements of serum C4 level could not substantially improve the identification of A*Q0 or B*Q0. C4 dependent activity in radial diffusion hemolysis showed satisfactory correspondence with the number of expressed C4B alleles. At least three haplotypes with two C4A genes (duplicated A genes) were observed as ascertained from offspring analysis in accordance with the MHC segregation pattern. Individuals with the duplicated C4A gene (C4A*3. A*2. in the absence of any other expressed A allele or together with C4A*92) showed only partial inhibition of Rodgers antisera. Partial inhibition of Chido antisera was seen in individuals with C4B 2 (in the absence of other B allotypes). The findings support the hypothesis of at least two structural C4 loci. The also demonstrate the inconsistency of quantitative data in the recognition of silent alleles. 相似文献
29.
The distribution of poly(A)+ mRNA among polysomes, monosomes, and ribosome-free supernatant fractions after mengovirus infection of Ehrlich ascites tumor (EAT) cells was investigated employing sucrose gradient centrifugation of their corresponding postnuclear supernatants. Poly(A)+ mRNA was isolated from sucrose gradient fractions and quantitated in a cell-free protein synthesizing system from uninfected EAT cells. It was also localized by annealing [3H]-poly(U) to the poly(A)-tracts of mRNA present in the sucrose gradient fractions. Both experiments revealed a gradual shift of host poly(A)+ mRNA from large to small polysomes and monosomes, respectively, with the time postinfection. The greatest part of host template RNA appears to remain ribosome-bound and only a fraction seems to be detached from the ribosomes in the course of mengovirus infection. At the end of the infectious cycle, 8 h postinfection, approximately 70% of the poly(A)+ mRNA detected in uninfected cells is still biologically active, but not translated in vivo, in agreement with data from the [3H] poly(U) hybridization experiment. 相似文献
30.
Behm C. A. and Bryant C. 1982. Phosphoenolpyruvate carboxykinase from Fasciola hepatica. International Journal for Parasitology12: 271–278. The kinetic properties of a partially purified preparation of phosphoenolpyruvate carboxykinase (PEPCK) from F. hepatica were examined. The pH optimum for the carboxylation reaction is 5.8–6.2. The enzyme is more active with Mn2+ than Mg2+ and the Mn2+ saturation curve was sigmoid. Apparent Km values for the substrates GDP, IDP, PEP and HCO3? were determined and found to be in the same range as those reported for other helminths except that the enzyme is less sensitive to low PEP concentrations. GTP and ATP at 0.5 and 1.0 mM inhibit the enzyme; the GTP inhibition was greater in the presence of Mg2+ than Mn2+ and was competitive with GDP. It was concluded that the activity of PEPCK from F. hepatica is controlled by the concentration of reactants and the ambient pH, that the accumulation of GTP is a sensitive mechanism for inhibiting the carboxylation reaction and that PEPCK activity in the cytosol is likely to be favoured over that of pyruvate kinase except when pH is high and PEP concentration low. 相似文献