976 resultados para Vita Mark II
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Microfilm.. Valencia: BV, ca. 1990.
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Microfilm.. Valencia: BV, ca. 1990.
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Microfilm.. Valencia: BV, ca. 1990.
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Cross-linked antigens on the surface of a motile cell cap at the trailing end of the cell. In Dictyostelium discoideum, myosin II null mutants have previously been reported to be unable to cap Con A receptors, although they are able to locomote. This finding implicated myosin II as an essential component of the capping mechanism, although not of the machinery for locomotion. Here we show that myosin II null mutants do cap Con A receptors, albeit less efficiently than does wild type. This shows that cap formation is not absolutely dependent on myosin II and that a close mechanistic relationship between capping, particle movement, and cell migration may still exist.
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Superoxide anion (O2−) plays a key role in the endogenous suppression of endothelium-derived nitric oxide (NO) bioactivity and has been implicated in the development of hypertension. In previous studies, we found that O2− is produced predominantly in the adventitia of isolated rabbit aorta and acts as a barrier to NO. In the present studies, we characterize the enzyme responsible for O2− production in the adventitia and show that this enzyme is a constitutively active NADPH oxidase with similar composition as the phagocyte NADPH oxidase. Constitutive O2−-generating activity was localized to aortic adventitial fibroblasts and was enhanced by the potent vasoconstrictor angiotensin II. Immunohistochemistry of aortic sections demonstrated the presence of p22phox, gp91phox, p47phox, and p67phox localized exclusively in rabbit aortic adventitia, coincident with the site of staining for O2− production. Furthermore, immunodepletion of p67phox from adventitial fibroblast particulates resulted in the loss of NADPH oxidase activity, which could be restored by the addition of recombinant p67phox. Further study into the regulation of this adventitial source of O2− is important in elucidating the mechanisms regulating the bioactivity of NO and may contribute to our understanding of the pathogenesis of hypertension.
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Purified RNA polymerase II initiated transcription from the yeast CUP1 promoter fused to a C-less cassette if the DNA was negatively supercoiled. Relaxed plasmid was not transcribed. Transcription did not require addition of any other transcription factors. TATA box-binding protein (TBP) was not detectable in the polymerase preparation and the TATA box was not required. Deletion analysis of the CUP1 promoter revealed that a 25-bp element containing the initiation region was sufficient for recognition by polymerase. Two transcription start sites were mapped, one of which is identical to one of the two major start sites observed in vivo. Our observations can be accounted for by using a theoretical analysis of the probability of DNA melting within the plasmid as a function of superhelix density: the CUP1 initiation element is intrinsically unstable to superhelical stress, permitting entry of the polymerase, which then scans the DNA to locate the start site. In support of this analysis, the CUP1 promoter was sensitive to mung bean nuclease. These observations and a previous theoretical analysis of yeast genes support the idea that promoters are stress points within the DNA superhelix. The role of transcription factors might be to mark the promoter and to regulate specific melting of promoter DNA.
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The yeast transcriptional repressor Tup1, tethered to DNA, represses to strikingly different degrees transcription elicited by members of two classes of activators. Repression in both cases is virtually eliminated by mutation of either member of the cyclin-kinase pair Srb10/11. In contrast, telomeric chromatin affects both classes of activators equally, and in neither case is that repression affected by mutation of Srb10/11. In vitro, Tup1 interacts with RNA polymerase II holoenzyme bearing Srb10 as well as with the separated Srb10. These and other findings indicate that at least one aspect of Tup1's action involves interaction with the RNA polymerase II holoenzyme.
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We have changed the potential phosphorylation site, a threonine residue at position 2 of the D2 polypeptide of the photosystem II complex of Chlamydomonas reinhardtii, to alanine, valine, aspartate, proline, glycine, or glutamate. Mutants with neutral amino acid changes did not display any phenotype with regard to photoautotrophic growth, light sensitivity, fluorescence transients, or photoinhibition. Pulse labeling of these mutants with 32P indicated that a phosphorylated protein of the same size as D2 is absent in these mutants, suggesting that threonine-2 is indeed the unique phosphorylation site of D2. In contrast, mutants in which threonine-2 has been replaced with acidic residues are deficient in photosystem II. Use of chimeric genes containing the psbD 5′-untranslated region revealed that the initiation of translation was not affected in these mutants, but the mutations interfered with a later step of D2 synthesis and accumulation.
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We have produced and analyzed transgenic birdsfoot trefoil (Lotus corniculatus L.) plants harboring antisense dihydroflavonol reductase (AS-DFR) sequences. In initial experiments the effect of introducing three different antisense Antirrhinum majus L. DFR constructs into a single recipient genotype (S50) was assessed. There were no obvious effects on plant biomass, but levels of condensed tannins showed a statistical reduction in leaf, stem, and root tissues of some of the antisense lines. Transformation events were also found, which resulted in increased levels of condensed tannins. In subsequent experiments a detailed study of AS-DFR phenotypes was carried out in genotype S33 using pMAJ2 (an antisense construct comprising the 5′ half of the A. majus cDNA). In this case, reduced tannin levels were found in leaf and stem tissues and in juvenile shoot tissues. Analysis of soluble flavonoids and isoflavonoids in tannin down-regulated shoot tissues indicated few obvious default products. When two S33 AS-DFR lines were outcrossed, there was an underrepresentation of transgene sequences in progeny plants and no examples of inheritance of an antisense phenotype were observed. To our knowledge, this is the first report of the genetic manipulation of condensed tannin biosynthesis in higher plants.
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Photoactivation of caged fluorescent tubulin was used mark the microtubule (MT) lattice and monitor MT behavior in interphase cells. A broadening of the photoactivated region occurred as MTs moved bidirectionally. MT movement was not inhibited when MT assembly was suppressed with nocodazole or Taxol; MT movement was suppressed by inhibition of myosin light chain kinase with ML7 or by a peptide inhibitor. Conversely, MT movement was increased after inhibition of cytoplasmic dynein with the antibody 70.1. In addition, the half-time for MT turnover was decreased in cells treated with ML7. These results demonstrate that myosin II and cytoplasmic dynein contribute to a balance of forces that regulates MT organization, movement, and turnover in interphase cells.
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The Danish Expedition of the "Galathea II" around the world brought important results concerning the marine organisms in the deep sea. The "Galathea II" showed not only different organisms of the Abyssal but for the first time of the deepest trenches of the western Pacific. Anton Bruun coined the term Hadal for the region below the Abyssal under 6000 m. Although the "Galathea II" aimed to investigate new deep sea regions beside the routes of former expeditions and to widen the horizon of knowledge relating marine organisms the technical equipment and the methodological approach had partly been developed earlier. The expedition of the "Galathea II" is part of a long tradition of cruises such as that of the British "Challenger", the German "Valdivia" and the Swedish "Albatross" and especially the Danish cruises of the "Dana I" and "Dana II" which happened some years before.
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The eleventh research cruise of Japanese Geodynamics Project in the West Pacific was carried out by the R/V Tokaidaigaku-maru II in August, 1974. During this cruise, in which the authors participated, many traverses of echo sounding and seismic reflection profiling and frequent sampling of bottom sediments were undertaken.
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Cavagna 10582: Bound with thirteen other Italian and Latin works, most from the 19th century; binder's title: "Opuscoli"; former shelf-mark Cavagna 10585.
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Includes index.