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排序方式: 共有388条查询结果,搜索用时 15 毫秒
101.
Michelle Moritz Yixian Zheng Bruce M. Alberts Karen Oegema 《The Journal of cell biology》1998,142(3):775-786
Extracting isolated Drosophila centrosomes with 2 M KI generates salt-resistant scaffolds that lack the centrosomal proteins CP190, CP60, centrosomin, and γ-tubulin. To clarify the role of these proteins in microtubule nucleation by centrosomes and to identify additional centrosome components required for nucleation, we have developed an in vitro complementation assay for centrosome function. Centrosome aster formation is reconstituted when these inactive, salt-stripped centrosome scaffolds are supplemented with a soluble fraction of a Drosophila embryo extract. The CP60 and CP190 can be removed from this extract without effect, whereas removing the γ-tubulin destroys the complementing activity. Consistent with these results, we find no evidence that these three proteins form a complex together. Instead, γ-tubulin is found in two distinct protein complexes of 240,000 and ∼3,000,000 D. The larger complex, which is analogous to the Xenopus γ-tubulin ring complex (γTuRC) (Zheng, Y., M.L. Wong, B. Alberts, and T. Mitchison. 1995. Nature. 378:578–583), is necessary but not sufficient for complementation. An additional factor found in the extract is required. These results provide the first evidence that the γTuRC is required for microtubule nucleation at the centrosome. 相似文献
102.
Repeated evolution of an acetate-crossfeeding polymorphism in long-term populations of Escherichia coli 总被引:1,自引:0,他引:1
Six out of 12 independent replicate populations of Escherichia coli
maintained in long-term glucose-limited continuous culture for up to
approximately 1,750 generations evolve polymorphisms maintained by acetate
crossfeeding. In all cases, the acetate-crossfeeding phenotype is
associated with semiconstitutive overexpression of acetyl CoA synthetase,
which allows for the enhanced uptake of low levels of exogenous acetate.
Mutations in the 5' regulatory region of the acetyl CoA synthetase locus
are responsible for all the acetate crossfeeding phenotypes found. These
changes were either transposable-element insertions or a single T-->A
nucleotide substitution at position -93 relative to the acs gene
translation start site.
相似文献
103.
Belinda Reyers Alberts S. Van Jaarsveld Melodie A. McGEOCH Alexander N. James 《Biodiversity and Conservation》1998,7(7):945-965
Due to the shortage of financial resources for international conservation assistance, the setting of priorities for this assistance is an important issue. A national biodiversity risk assessment index (NABRAI) is constructed to quantify national conservation performances and identify nation states of critical conservation concern. The index, which contains measures of biodiversity stock, flow and response measures, attempts to overcome several weaknesses present in other models used to prioritize nations for conservation assistance. Multivariate analyses of the index as well as economic and biodiversity resources reveal significant positive correlations between the NABRAI values and population density as well as land area exposed to high disturbance intensity. The combination of the multivariate analyses and the interpretation of NABRAI values allows for prioritization of biodiversity risk among the global community and can thus serve as an indicator of current priorities for policy makers. The present study also suggests two methods to incorporate a better understanding of biodiversity risk in models of conservation priorities; by including a wider range of variables and by developing a theoretical foundation for the relationship between the categories of variables used in the model. 相似文献
104.
Meinkoth Judy L. Alberts Arthur S. Went Wei Fantozzi Dominic Taylor Susan S. Hagiwara Masatoshi Montminy Marc Feramisco James R. 《Molecular and cellular biochemistry》1993,127(1):179-186
Molecular and Cellular Biochemistry - Temporal cellular events responsible for hormonal activation of responses mediated by the cAMP-dependent protein kinase (PKA) have been studied in living... 相似文献
105.
The extraction and purification methods used in the maleyl derivatization HPLC technique was evaluated with respect to the pH of the extraction mixture, the extraction solvent and the purification methods used in order to determine optimum conditions for quantification of fumonisins B1, B2, and B3 in corn cultures. The highest recovery of the three compounds was obtained by extraction at pH 3.5 with CH3OH–H20 (3∶1), whilst the subsequent solvent partitioning and reversedphase C18 Sep-pak purification have been shown to be very important in the quantification of the fumonisins in the corn cultures. The percentage recovery of the improved technique, utilizing a gradient HPLC solvent system for the simultaneous determination of the fumonisins, was 93.4% for FB1, 68.0% for FB2, and 82.6% for FB3. The study indicates that the polarity of the fumonisins and consequently their solubility during extraction as well as their behavior during the subsequent purification step play an important role in quantification of these mycotoxins in corn cultures. 相似文献
106.
J. F. Alberts W. C. A. Gelderblom W. F. O. Marasas J. P. Rheeder 《Mycotoxin Research》1994,10(2):107-115
Production of fumonlsins B1 (FB1) and B2 (FB2) by 5 lyophillzation batches ofFusarium moniliforme strain MRC 826 was studied in several liquid media and vermlculite supplemented with liquid media. In addition the effect of different parameters including pH, Inert material, shake versus stationary cultures as well as different carbon sources on the production of the fumonlsins were investigated. Fumonlsin production in liquid cultures was significantly (P<0.01) correlated (r=0.92–0.98) with fungal growth, which in turn is affected by the pH of the medium as well as the carbon source utilized. The highest FB1 yields (approximately 40 mg/l) over the incubation period of 14 days were produced in a chemically defined medium with glucose as carbon source set at an initial pH value of 4. FB1 production in “corn patty” cultures (approximately 1 to 3 g/kg), however, by far exceeded that obtained in the liquid media, while poor fungal growth and fumonlsin production was obtained in vermlculite supplemented cultures. From these studies it became clear that the ability of a culture to produce fumonlsins is determined by the interaction of a variety of physiological and nutritional factors regarding the inoculum and the culture medium. 相似文献
107.
108.
A simple technique has been developed for isolating intracellular DNA and its bound proteins from uninfected and phage-infected bacteria. This technique, which utilizes aqueous salt concentrations in the physiological range, is based upon the fact that DNA exists in normal cell lysates in a stiff random coil conformation, and has an unusually large excluded volume to mass ratio. Such stiff coils display a unique combination of low sedimentation coefficient and large Stokes radius, enabling them to be separated rapidly from all other cellular components by successive centrifugal and gel permeation steps. Analysis of this purified intracellular DNA fraction from bacteriophage T4-infected Escherichia coli reveals mainly DNA and protein, with a small amount of RNA also present. Among the major proteins obtained are the DNA-dependent RNA polymerase of the host and the products of T4 genes rIIA, rIIB, and 32 (DNA-"unwinding" protein). Small amounts of the proteins coded by T4 genes 43 (DNA polymerase) and 42 (dCMP hydroxymethylase) have also been identified, in addition to at least 13 other phage-coded proteins of unidentified genes. Much of the phage-coded protein in the complex, including the gene 32 protein, does not exchange readily with the same protein exogenously added in the lysate. 相似文献
109.
Rabbits fed a wheat starch-casein diet develop a marked hypercholesterolemia with a lipoprotein distribution similar to that of humans. Approximately 76% of the total cholesterol is carried in the low density lipoprotein (LDL) fraction (1.006 less than d less than 1.063 g/ml). Inclusion of 1% cholestyramine in the diet prevents the increase in plasma cholesterol. The cholestyramine effect is mediated through an increased fractional catabolic rate of 125I-LDL. In order to determine the potential role of hepatic LDL receptors in the removal of LDL from the plasma, binding of 125I-LDL and 125I-beta-VLDL (beta-migrating very low density lipoproteins) to hepatic membranes prepared from livers of rabbits fed the wheat starch-casein diet with or without cholestyramine supplementation was investigated. Membranes from livers of the cholestyramine-supplemented animals exhibit high levels of specific EDTA-sensitive binding of either of the 125I-labeled lipoproteins. Very little EDTA-sensitive binding occurs on liver membranes from wheat starch-casein-fed rabbits that have not been treated with cholestyramine. These results indicate that the hypercholesterolemia in rabbits associated with the wheat starch-casein diet is wholly or partially the result of a decreased number of specific hepatic LDL receptors and thus a decreased catabolism of plasma cholesterol. The response of the liver to the inclusion in the diet of the bile acid sequestrant, cholestyramine, is to maintain or increase the number of specific LDL binding sites, thus promoting catabolism of plasma cholesterol. 相似文献
110.
Fackler OT Lu X Frost JA Geyer M Jiang B Luo W Abo A Alberts AS Peterlin BM 《Molecular and cellular biology》2000,20(7):2619-2627
The activation of Nef-associated kinase (NAK) by Nef from human and simian immunodeficiency viruses is critical for efficient viral replication and pathogenesis. This induction occurs via the guanine nucleotide exchange factor Vav and the small GTPases Rac1 and Cdc42. In this study, we identified NAK as p21-activated kinase 1 (PAK1). PAK1 bound to Nef in vitro and in vivo. Moreover, the induction of cytoskeletal rearrangements such as the formation of trichopodia, the activation of Jun N-terminal kinase, and the increase of viral production were blocked by an inhibitory peptide that targets the kinase activity of PAK1 (PAK1 83-149). These results identify NAK as PAK1 and emphasize the central role its kinase activity plays in cytoskeletal rearrangements and cellular signaling by Nef. 相似文献