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71.
AVRAM HERSHKO PIERRE MAMONT ROBERT SHIELDS GORDON M. TOMKINS 《Nature: New biology》1971,232(33):206-211
A hypothesis has been developed to relate stringent control in bacteria to a set of interactions involved in the regulation of growth of transformed and untransformed mammalian cells. 相似文献
72.
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
73.
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
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77.
Perin L. Donnini M. Diomede L. Romano M. Tacconi M. T. Luisetti M. Salmona M. 《Cytotechnology》1991,7(1):25-32
An expression vector for G-CSF, pASLB3-3, was constructed and introduced into Namalwa KJM-1 cells (Hosoi et al., 1988), and cells resistant to 100 nM of methotrexate (MTX) were obtained. Among them, the highest producer, clone SC57, was selected and the productivity of this clone was further characterized. The maximal production of G-CSF was at the most 1.8 g/ml/day using a 25 cm2 tissue culture flask, even though the cell number was above 7×105 cells/ml. The limiting factors at high density were analyzed as the deficiency of nutrients, such as glucose, cysteine and serine, and pH control. The depression of specific G-CSF productivity per cell under the batch culture conditions was overcome by using a perfusion culture system, BiofermenterTM (Sato, 1983) with modifications of nutrients supplementation by a dialysis membrane and/or dissolved oxygen (DO) supplementation by microsilicone fibers. ITPSGF medium was modified to elevate concentrations of amino acids and glucose by 2.0- and 2.5-times, respectively. Under the control of pH at 7.4 and DO at 3 ppm, the specific G-CSF productivity was not depressed even at high cell density (above 1×107 cells/ml), and the amount of G-CSF reached 41 g/ml. These results indicated the possibility of finding the optimum culture conditions for the production of recombinant proteins by Namalwa KJM-1 cells.Abbreviations ABTS
2,2-Azino-di-(3-ethylbenzothiazoline)-6-sulfonic acid
- BSA
Bovine Serum Albumin
- BSA-PBS
Phosphate-buffered Saline without Ca2+ and Mg2+ containing Bovine Serum Albumin
- dhfr
Dihydrofolate Reductase
- DO
Dissolved Oxygen
- G-CSF
Granulocyte Colony-stimulating Factor
- HEPES
4-(2-Hydroxyethyl)-1-piperazineethansulfonic Acid
- IFN
Interferon
- MTX
Methotrexate
- PBS(-)
Phosphate-buffered saline without Ca2+ and Mg2+
- Tween-PBS
Phosphate-buffered saline without Ca2+ and Mg2+ containing 0.05% of Tween 20 相似文献
78.
Feroze N. Ghadially Jean-Marie A. Lalonde Sue Yang-Steppuhn 《Virchows Archiv. B, Cell pathology including molecular pathology》1982,39(1):21-30
Cultured rabbit kidney cells were exposed to uranyl acetate. This produced single-membrane-bound presumably lysosomal bodies (called 'uraniosomes') containing electron-dense crystals in the cultured cells. Similar crystalline deposits were seen in extracellular locations also. All uraniosomes and extracellular uranium deposits analyzed by electron-probe x-ray analysis were found to contain uranium, potassium, calcium and phosphorus. Traces of sulphur were detected in some but not all uraniosomes and extracellular uranium deposits. 相似文献
79.
To investigate behavioural mechanisms that regulate the spacing of individuals, we studied aggression, approach, and avoidance of captive male juncos (Junco hyemalis) in relation to the distance between individuals. We measured behavioural tendencies by analysing the terminations of social states so as to determine the instantaneous probability rates of terminal actions. These rates permit accurate comparisons of behavioural tendencies in different social situations. An individual's tendencies to supplant, approach, or withdraw from an opponent depended on the dominance relationship of the two birds and on the distance between them. Interactions did not vary with the magnitude of the difference between opponents' ranks. The dependence of aggression, approach, and avoidance on the distance between opponents controls the spacing of individuals. 相似文献
80.
Neonatal Balb/c mice were suppressed forthe H8/T15 idiotype by injection of homologous anti-H8 (D. S. Strayer, D. A. Rowley, and H. Köhler, et al J. Immunol.114, 722, 1975. Six to eight weeks later groups of these suppressed mice were immunized up to three times with isologous anti-H8 raised in Balb/c. After a rest of 4 weeks each group was challenged with R36a vaccine and bleedings were obtained before and after this challenge. All sera were assayed for total anti-PC and H8 idiotype amounts by solid-phase radioimmunoassay. After two-preimmunizations with isologous anti-H8 no increase of the H8 levels was observed though these mice responded to R36a immunization with an increase of total anti-PC antibodies. After the third preimmunization, however, the H8 idiotype was increased in sera taken before and after challenge with R36a. These findings demonstrate that the state of neonatal idiotype suppression can be broken by immunization with complementary anti-idiotype. 相似文献