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91.
Kimball and Wilson1 reported that the arabinose analogue of cytidine (ara-C) inhibited DNA polymerase in a crude extract prepared from Ehrlich ascites cells. Furth and Cohen2 observed cytosine arabinoside triphosphate (ara-CTP) inhibited DNA polymerase in extracts from either calf thymus or bovine lymphosarcoma tissue, although these investigators3 had already found no effect of ara-CTP on DNA polymerase from Escherichia coli. The inhibition in both of these cases could be substantially reversed by dCTP; but incorporation of the arabinose nucleotide (ara-CMP) into DNA could not be unequivocally demonstrated. Graham and Whitmore4 reported the incorporation of ara-C into DNA in vivo and the inhibition of a DNA polymerase from L cells by ara-CTP. They found that ara-CMP was initially incorporated into small DNA strands but subsequently appeared in long strands. Momparler5 has presented evidence that, in vitro, ara-C incorporation was limited to the 3′-hydroxyl end of DNA chains. Such incorporation might be expected to block further chain elongation but this expectation was not supported by the evidence presented by Graham and Whitmore. 相似文献
92.
ALINA TAYLOR 《Nature: New biology》1971,234(48):144-145
JACOB and Fuerst1,2 demonstrated the presence of a bacteriolytic enzyme (λ-endolysin) in the induced cultures of lysogenic Escherichia coli K12 (λ). The enzyme was later identified as the product of gene R; of phage λ3 which is involved in bacterial lysis at the end of a latent period. The enzyme is apt to form spheroplast-like structures in E. coli2 and one would therefore expect its substrate to be murein. 相似文献
93.
Summary Labelling of renal tubule cytosomes with electron dense iron granules can be attained by daily intramuscular injections to mice of an iron sorbitol citric-acid compound in a total of approximately 50 mg Fe+++/100 g of body weight. The labelled cytosomes correspond to secondary lysosomes and represent heterolysosomes or ambilysosomes. The evidence suggests that tubule and lysosome function are undisturbed by the labelling procedure. The use of this method for fine structural studies of the interaction between secondary lysosomes and other cytoplasmic organelles and elements is indicated.Microbodies do not incorporate administered Fe+++. The morphological observations support the opinion that these bodies are formed in specialized portions of the smooth surfaced endoplasmic reticulum of proximal tubule cells.Supported in part by grants from the Swedish Medical Research Council (Projects No. K 67-12x-1006-2, B 67-12x-1006-02K, K 68-12x-1006-03, and B 69-12x-1006-04A). The assistance of Miss Silwa Mengarelli and Miss Britt-Marie Pettersson is gratefully acknowledged. 相似文献
94.
95.
An investigation was made of the anatomical structure of the shoot apex ofSenecio vulgaris L. a photoperiodically neutral plant, and compared with the formation of successive leaf primordia along the axis up to the initiation of the terminal inflorescence. In the shoot apex of a germinating plant a central zone can first be distinguished from the peripheral zone which is composed of small and intensely stained cells. Later, a rib meristem appears. At the time of the initiation of the middle (the largest) leaves, the shoot apex has a distinct small central zone and a well developed peripheral zone and rib meristem. Between these zones there is a group of cells dividing in all directions, the subcentral zone. At the time of initiation of the last leaves, the central zone extends to the flanks and gradually ceases to be distinguishable. At the same time, the subcentral zone increases in size. This is caused first by cell division and later, with the initiation of the last, most reduced leaves, by enlargement of the cells. Vacuolization in the inner part of the apex and the arrangement of the superficial cells in rows parallel to the surface of the apex, is a preparatory step to the initiation of the inflorescence. 相似文献
96.
97.
Jan O. Gordeladze Trine Haugen Eivind J. Paulssen Ruth H. Paulssen 《Bioscience reports》1996,16(1):65-74
The presence of the pertussis toxin (PTX) insensitive GTP-binding proteins (G-proteins) Gq and/or G11 has been demonstrated in three different prolactin (PRL) and growth hormone (GH) producing pituitary adenoma cell lines. Immunoblocking of their coupling to hormone receptors indicates that Gq and/or G11 confer throliberin (TRH) responsive phospholipase C (PL-C) activity in these cells. The contention was substantiated by immunoprecipitation analyses snowing that anti Gq/11-sera coprecipitated PL-C activity. In essence, only Gq/11 (but neither Gi2, Gi3 nor Go) seems to mediate the TRH-sensitive PL-C activity, while Go may be coupled to a basal or constitutive PL-C activity. Immunoblocking studies imply that the B-complex also, to some extent, may stimulate GH3 pituitary cell line PL-C activity. Finally, the steady state levels of Gq/11 mRNA and protein were downregulated upon long term exposure of the GH3 cells to TRH (but not to vasoactive intestinal peptide = VIP). 相似文献
98.
Jan Lepš 《Folia Geobotanica》1995,30(4):455-459
Variance deficit in the number of species per sampling unit, as compared to a null model with species occurring independently of each other has been considered by various authors to be evidence for niche limitation. I show that simpler mechanisms could explain this phenomenon. Of those, the competition of individuals for space limits the number of individuals per sampling unit, resulting in decrease of variance in species richness. Testing the proportions of species belonging to various guilds seems to be more ecologically interesting, although here also the variance deficit can hardly be taken as reliable evidence for niche limitation. 相似文献
99.
100.
Changes in basin geomorphology after implementation of the Oosterschelde estuary project 总被引:8,自引:8,他引:0
The completion in 1986/87 of an open storm-surge barrier in the inlet and of secondary dams in the landward parts of the Oosterschelde tidal basin (SW Netherlands) has had and will continue to have a significant impact on geomorphological developments. An analysis of historic data, and of recent detailed bathymetric and morphodynamic process data, indicates that former trends have reversed. At present the Oosterschelde is a sedimentation basin with a degrading intertidal area and silting up of channels. The continuing reduction in intertidal area, the decreasing geomorphological gradients, the increasing fine sediment content of channel deposits, combined with a general reduction in hydrodynamics, imply significant ecological effects. 相似文献