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191.
The polytenization of rRNA cistrons in Drosophila species is studied in an attempt to follow the course of under-representation of heterochromatic compared with euchromatic chromosome regions. 相似文献
192.
Structure of the Purple Membrane 总被引:34,自引:0,他引:34
IN the preceding article1 it has been shown that a cell membrane fragment, the purple membrane, isolated from Halobacterium halobium2 contains retinal bound in a mole ratio of 1 : 1 to a protein of molecular weight 26,000 which is the only protein present. We now describe the structure of the purple membrane and its localization in the bacterial cell envelope. 相似文献
193.
194.
Virus Specific RNA in Cells transformed by RNA Tumour Viruses 总被引:21,自引:0,他引:21
Virus specific RNA comprises 5% of the nuclear RNA and 0.5–1.0% of the cytoplasmic RNA of cells transformed by murine sarcoma viruses. Even cryptically transformed cells which possess no detectable virus or viral proteins synthesize detectable amounts of viral RNA. 相似文献
195.
196.
Cell-free Studies on the Regulation of the Arabinose Operon 总被引:17,自引:0,他引:17
A DNA directed, cell-free system which synthesized L-ribulokinase coded by the L-arabinose operon ara OIBAD, has been developed. L-arabinose but not the araC gene product is required for the expression of this operon and, in addition, cyclic AMP and guanosine tetraphosphate are needed for optimal synthesis. 相似文献
197.
198.
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
199.
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
200.
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