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21.
Derepression of Phosphomannose Isomerase by Regulator Gene Mutations Involved in Capsular Polysaccharide Synthesis in Escherichia coli K-12 总被引:16,自引:11,他引:5
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A regulator gene mutation (capR) that causes increased synthesis of capsular polysaccharide and derepressed synthesis of several enzymes involved in polysaccharide synthesis also derepresses phosphomannose isomerase (PMI) synthesis. In contrast, a second mutation (capS, which maps separately from capR) that causes increased production of the same polysaccharide does not lead to increased synthesis of PMI (nor of several of the other enzymes involved in polysaccharide synthesis). Introduction of the capR9 allele by transduction or mutation of capR(+) to capR can change the phenotype of a mannose-negative nonmucoid strain to a mannose-positive mucoid phenotype. Thus, genotype capR(+)man-2 is mannose-negative and nonmucoid, but genotype capR9 man-2 is mannose positive and mucoid. Other interactions between these alleles in the synthesis of capsular polysaccharide are recorded. 相似文献
22.
The ATP-binding-cassette transmembrane transporters (ABC transporters)
known from vertebrates belong to four major subfamilies: (1) the P-
glycoproteins (Pgp); (2) the cystic fibrosis transmembrane conductance
regulators (CFTR); (3) the Tap proteins encoded with the major
histocompatibility complex of mammals; and (4) the peroxisomal membrane
proteins. Both Pgp and CFTR have a structure suggesting a past internal
gene duplication; a phylogenetic analysis indicated that these duplications
occurred independently, while an independent tandem gene duplication
occurred in the case of the Tap family. Both the Pgp and Tap proteins show
evidence of relationship to bacterial ABC transporters lacking internal
duplication, and both are significantly more closely related to the HlyB
and MsbA families of transporters from purple bacteria than they are to ABC
transporters from nonpurple bacteria. The simplest hypothesis to explain
this observation is that eukaryotic Pgp and Tap genes are descended from a
mitochondrial gene or genes that were subsequently translocated to the
nuclear genome. The Pgp genes of eukaryotes are characterized by a
remarkable degree of convergent evolution between the ATP-binding cassettes
of their N- terminal and C-terminal halves, whereas no such convergence is
seen between the two halves of CFTR genes or between the duplicated Tap
genes. Exon 13 of the CFTR gene, which encodes a putative regulatory domain
not found in other ABC transporters apart from CFTR, showed high levels of
both synonymous and nonsynonymous difference in comparisons among different
mammalian species, suggesting that this region is a mutational hot spot.
相似文献
23.
24.
X Xiao G Hintermann AL Demanin J Piret 《Journal of industrial microbiology & biotechnology》1996,16(4):261-262
Streptomyces glaucescens is shown to possess -lactamase activity which is inhibitable by clavulanate. This is important in regard to its use as a cloning host for enzymes of \-lactam biosynthesis. 相似文献
25.
H. C. Rosenbaum M. G. Egan P. J. Clapham R. L. BrownellJr & R. DeSalle 《Molecular ecology》1997,6(7):677-681
DNA was isolated from an early twentieth century museum specimen of northern right whale baleen. A system of stringent controls and a novel set of cetacean specific primers eliminated contamination from external sources and ensured the authenticity of the results. Sequence analysis revealed that there were informative nucleotide positions between the museum specimen and extant members of the population and closely related species. The results indicate that museum specimens of baleen can be used to assess historical genetic population structure of the great whales. 相似文献
26.
Brain actin extracted from an acetone powder of chick brains was purified by a cycle of polymerization-depolymerization followed by molecular sieve chromatography. The brain actin had a subunit molecular weight of 42,000 daltons as determined by co-electrophoresis with muscle actin. It underwent salt-dependent g to f transformation to form double helical actin filaments which could be "decorated" by muscle myosin subfragment 1. A critical concentration for polymerization of 1.3 microM was determined by measuring either the change in viscosity or absorbance at 232 nm. Brain actin was also capable of stimulating the ATPase activity of muscle myosin. Brain myosin was isolated from whole chick brain by a procedure involving high salt extraction, ammonium sulfate fractionation and molecular sieve chromatography. The purified myosin was composed of a 200,000-dalton heavy chain and three lower molecular weight light chains. In 0.6 M KCl the brain myosin had ATPase activity which was inhibited by Mg++, stimulated by Ca++, and maximally activated by EDTA. When dialyzed against 0.1 M KCl, the brain myosin self-assembled into short bipolar filaments. The bipolar filaments associated with each other to form long concatamers, and this association was enhanced by high concentrations of Mg++ ion. The brain myosin did not interact with chicken skeletal muscle myosin to form hybrid filaments. Furthermore, antibody recognition studies demonstrated that myosins from chicken brain, skeletal muscle, and smooth muscle were unique. 相似文献
27.
E W Jabs C A Coss S J Hayflick T E Whitmore R M Pauli S J Kirkpatrick D A Meyers R Goldberg D W Day K N Rosenbaum 《Genomics》1991,11(1):188-192
Treacher Collins syndrome is an autosomal dominant condition of bilateral craniofacial abnormalities of structures derived from the first and second branchial arches. A patient with severe manifestations of Treacher Collins syndrome and a de novo chromosomal deletion in region 4p15.32----p14 was identified. Anonymous DNA sequences of loci D4S18, D4S19, D4S20, D4S22, and D4S23 were mapped to the deleted region. DNA probes previously mapped to loci on chromosome 4p (D4S10, D4S15, D4S16, D4S26, D4S35, D4S95, D4S144, RAF1P1, QDPR, and HOX7) were not deleted in this patient. Linkage analysis between the D4S18, D4S23, and QDPR loci and Treacher Collins syndrome in eight families excluded the Treacher Collins syndrome locus from the region of the deletion. 相似文献
28.
Multiple alpha- and beta-tubulin genes in Chlamydomonas and regulation of tubulin mRNA levels after deflagellation 总被引:41,自引:0,他引:41
We constructed and characterized recombinant cDNA clones containing alpha- and beta-tubulin DNA sequences. The inserted DNA was determined to code for alpha- and beta-tubulin by positive hybridization-selection. The selected mRNA was translated in vitro, and the translation products were shown to be alpha- or beta-tubulin by comigration with flagellar alpha- and beta-tubulin on one- and two-dimensional gels and by immunoprecipitation with antibodies specific for alpha- and beta-tubulin. Hybridization of the cloned tubulin probes with Chlamydomonas DNA indicated that there are at least two genes each for alpha- and beta-tubulin in this organism. No evidence of cross-hybridization between alpha- and beta-tubulin DNA sequences was found. Because previous experiments had shown that tubulin synthesis was stimulated in response to flagellar amputation, the tubulin clones were used to analyze the levels of tubulin sequences in RNA from cells before and after deflagellation. Hybridization of the tubulin cDNA probes with total or polyadenylated RNA indicated that tubulin sequences in RNA increased within 8 min following deflagellation, reached maximal levels by 50 min and began to decrease by 80 min after deflagellation. One hybridization band was detected with use of the beta-tubulin probe, but RNA in two size classes hybridized to the alpha-tubulin probe. 相似文献
29.
Giuseppe Colacicco Mukul K. Basu Apurba K. Ray Murray Wittner Robert M. Rosenbaum 《Prostaglandins & other lipid mediators》1977,14(2):283-294
Transformed cells from human lung carcinoma (Line A549), resembling type II pneumocytes, were cultured in monolayer at 37°C and incubated for five hours with 3H-choline and 14C-palmitate in the presence of various concentrations of prostaglandins (PGs) E2 and F2α. In the control (no PG) the level of % palmitate incorporation was 13.5 × as high as that of choline, after taking isotope dilution into account. Between the concentrations studied, 0.1 and 10 μM, both prostaglandins stimulated markedly the incorporation of both precursors, though choline up to 3 × better than palmitate. This was indicated by a change in the palmitate/choline incorporation ratio from 13.5 to as low as 4.2. At the lowest PG concentration, 0.1 μM, PGE2 was much more effective than PGF2α in stimulating the incorporation of both precursors. 相似文献
30.
ERIC S. BONO PATRICK SMOLINSKI AL CASAGRANDA JUNDE XU 《Computer methods in biomechanics and biomedical engineering》2013,16(2):125-131
The Shear-slip Mesh Update Method (SSMUM) is being used in flow simulations involving large but regular displacements of one or more boundaries of the computational domain. We follow up the earlier discussion of the method with notes on practical implementation aspects. In order to establish a benchmark problem for this class of flow problems, we define and report results from a two-dimensional viscous flow around a rotating stirrer in a square chamber. The application potential of the method is demonstrated in the context of biomedical design problem, as we perform an analysis of blood flow in a centrifugal left ventricular assist device, or blood pump, which involves a rotating impeller in a non-axisymmetric housing. 相似文献