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271.
Interactions between Marek's Disease Herpesvirus and Avian Leucosis Virus in Tissue Culture 总被引:3,自引:0,他引:3
A GROUP B herpesvirus is important in the aetiology of Marek's disease, a highly contagious lymphoproliferative disease of chickens1,2. Chicks inoculated with enveloped Marek's disease herpesvirus (MDHV), extracted from feather follicle epithelium of chickens with the disease, developed tumour-like aggregates of lymphoid cells in the viscera and frequently in the peripheral nerves3,4. Cultures of chicken embryo fibroblast (CEF) cells infected with MDHV develop discrete foci of altered cells5. Our data show that MDHV infection of cultures of CEF cells, previously infected with an avian leucosis virus (RAV-2), results in both a reduction in the number of MDHV foci and an increase in the complement fixing avian leucosis antigen (COFAL)6 titre. 相似文献
272.
WHEN BHK 21 hamster cells are infected with polyoma virus1, there is no vegetative growth of virus, but stably transformed cells appear. These transformed cells are more easily transplanted than BHK 21 cells; they initiate their growth cycle in otherwise restrictive cultural conditions such as the absence of serum, high density and suspension; they grow with random orientation and have exposed on their surfaces receptor sites for certain glycoprotein agglutinins2–5. The proportion of stably transformed cells is low, even after high doses of virus. But a much higher proportion (sometimes all cells) shows abortive transformation—changes characteristic of transformation, but which last only a few days. In suspension cultures, for example, most of the infected cells grow into small colonies of four to thirty-two cells6. In surface cultures deprived of serum DNA synthesis is initiated and the cells may then divide at least once7: they also temporarily lose the normal parallel orientation and develop the typical random appearance of transformed cells. Moreover, the polyoma nuclear T-antigen and also a surface antigen detected by immunofluorescence, appear temporarily in most polyoma infected BHK 21 cells8, while 3T3 cells exposed to SV40 virus show transient exposure of cell surface sites reacting with conconavalin A (ref. 9). 相似文献
273.
ROBERT LAW 《Nature: New biology》1971,231(23):186-187
AIKEN and Vane have reported1 the independent actions of angiotensin I (AI) and angiotensin II (AII) on various isolated smooth muscle preparations, including rat colon. Tney showed that the apparent contractile action of AI on these preparations depended primarily on its in situ conversion to All by “converting enzyme” and that when the activity of the enzyme was inhibited by a pentapeptide extracted from Bothrops jararaca venom, the residual contractile action, probably due to unchanged AI, was very small. I have investigated the action of synthetic tetradecapeptide renin substrates (TPRS) on rat colon, in the light of the known actions of AI and All. 相似文献
274.
275.
Cooperation between Carrier-reactive and Hapten-sensitive Cells <Emphasis Type="Italic">in vitro</Emphasis> 总被引:8,自引:0,他引:8
CHRISTINA CHEERS J. C. S. BREITNER MARGERY LITTLE J. F. A. P. MILLER 《Nature: New biology》1971,232(34):248-250
THE mechanism, known as the carrier effect, whereby immunity to one or more determinant groups enhances the response to other determinants on the same multivalent antigen, was first recognized in delayed hypersensitivity to haptens, in which, for an appreciable response, the hapten must be coupled to the same protein carrier for priming and challenge1, 2. Carrier specificity has also been demonstrated in the secondary antibody responses to hapten protein conjugates3. Two alternative hypotheses have been advanced to explain this specificity. The “local environment” hypothesis supposes that the hapten-sensitive cell recognizes both the hapten and the carrier determinants. However, the antihapten antibodies produced do not distinguish details of the carrier molecule and so do not reflect the specificity of the cellular receptor. Furthermore, inert spacer molecules inserted between hapten and carrier do not interfere with carrier specificity in the antibody response3. Reflecting current views on the cooperation between thymus-derived (T) and bone marrow derived (B) lymphocytes in the antibody response to various antigens4, the second hypothesis invokes two or more cells, one with receptors directed towards the hapten (hapten-sensitive cell), the others specific for the carrier molecule proper (carrier-reactive cells). Supporting this is the observation that pre-immunization to a particular protein carrier alone could potentiate the primary or secondary antihapten response to a hapten conjugated to that protein5. In an adoptive transfer system, moreover, the efficiency of antihapten antibody production by cells primed to a particular hapten-protein conjugate and stimulated with the hapten conjugated on a heterologous protein, is significantly enhanced by the introduction of cells primed to the heterologous carrier alone. Anti-carrier serum antibody does not cause such enhancement6. The carrier-reactive cells must therefore cooperate in increasing the efficiency of the hapten-sensitive cells in some way other than by providing humoral anti-carrier antibody. Recent work strongly suggests that carrier reactive cells are thymus-derived6, 7. 相似文献
276.
Function of the <Emphasis Type="Italic">rel</Emphasis> Gene in <Emphasis Type="Italic">Escherichia coli</Emphasis> 总被引:6,自引:0,他引:6
Sokawa et al. suggest that rel- strains of Escherichia coli possess abnormal protein synthesizing machinery, which cannot carry out normal protein synthesis when the supply of amino-acids is limited. 相似文献
277.
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
278.
RAFIQ WAZIRI 《Nature: New biology》1971,231(26):286-288
IN the abdominal ganglion of Aplysia californica, there are two types of inhibitory post-synaptic potentials (IPSPs). There are unitary short-lasting IPSPs which occur as the result of conductance changes during the movement of Cl? across the synaptic membrane—IPSPs which have definite equilibrium potentials and characteristics similar to those described for other neuronal systems1—and there are IPSPs which last much longer and may be much more effective in regulating the activity of the neurone, which Taue has called “inhibitions of long duration” (ILD)2,3. In Aplysia some of these long lasting inhibitory potentials are produced by conductance changes and have definite equilibrium potentials4. Long lasting inhibitions or “slow inhibitory potentials” as well as short lasting IPSPs have also been described in vertebrate sympathetic ganglia5, but in these, long lasting IPSPs are not accompanied by changes in membrane conductance. Some of the long lasting inhibitions (LLI) have been explained on the basis of an ATP-dependent electrogenic Na+ pump6. Presumably this ATP-dependent pump hyperpolarizes the membrane by causing an outflux of Na+ from the cell which is more rapid than the corresponding “active” influx of K+7. There is evidence now for the existence of such an electrogenic Na+ pump in some of the identified neurones of the abdominal ganglion of Aplysia californica8. Pinsker and Kandel9 have found some evidence that in these neurones the electrogenic Na+ pump is activated by the synaptic action of an identified cholinergic inhibitory interneurone, L10, producing the long lasting “late IPSP”. But Kehoe and Ascher10, although agreeing that the same interneurone (L10) produces both types of IPSPs in the follower neurones, have shown that the “late IPSP”9 is due to an increase in the K+ conductance and that it has an equilibrium potential around ?90 mV. I have found that in this abdominal ganglion there is another specific interneurone which is electrotonically coupled to L10 and which, when activated, produces a long lasting inhibition (LLI) in a number of follower neurones. Thus L10 produces the LLI or “late IPSP” in some follower neurones not directly, but through the mediation of another interneurone. 相似文献
279.
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
280.
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