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排序方式: 共有384条查询结果,搜索用时 62 毫秒
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M F Ahmad N Nasrin M K Bagchi I Chakravarty N K Gupta 《The Journal of biological chemistry》1985,260(11):6960-6965
The characteristics of yeast eukaryotic initiation factor 2 (eIF-2) and Co-eIF-2A have been studied and compared with those of the corresponding factors from rabbit reticulocytes. 1) Unlike eIF-2r, purified eIF-2y did not contain bound GDP. 2) Purified eIF-2y preparation contained GTPase activity and dephosphorylated GTP to GDP. 3) An anti-eIF-2r preparation which predominantly precipitated the gamma-subunit (Mr 54,000) of eIF-2r also precipitated the larger subunit (Mr 54,000) of eIF-2y. 4) Unlike eIF-2r, ternary complex formation by eIF-2y was not inhibited by Mg2+. 5) Both Co-eIF-2A20y and Co-eIF-2r significantly enhanced Met-tRNAf binding to eIF-2y and, again, Mg2+ did not have any effect on this stimulated Met-tRNAf binding to eIF-2y. 6) Both Co-eIF-2A20y and Co-eIF-2r were similarly effective in stimulating Met-tRNAf binding to eIF-2r in the absence of Mg2+. However, in the presence of Mg2+, Co-eIF-2A20y was significantly less effective than Co-eIF-2r as Co-eIF-2A20y did not promote displacement of GDP from eIF-2r X GDP. 7) eIF-2y bound [3H]GDP and this binding was significantly enhanced in the presence of Mg2+. Also, [3H]GDP in the preformed eIF-2y X [3H]GDP complex was rapidly exchanged with exogenously added unlabeled GDP in the presence of Mg2+. Co-eIF-2A20y had no effect on GDP binding to eIF-2y nor on GDP exchange reactions. 8) Reticulocyte heme-regulated protein synthesis inhibitor, which phosphorylated almost completely (in excess of 80%) the alpha-subunit (Mr 38,000) of eIF-2r, also phosphorylated similarly the smaller subunit (Mr 36,000) of eIF-2y. However, such phosphorylation had no significant effect on ternary complex formation, GDP binding, and GDP exchange reactions. 相似文献
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We have broadly defined the DNA regions regulating esterase6 activity in
several life stages and tissue types of D. melanogaster using P-
element-mediated transformation of constructs that contain the esterase6
coding region and deletions or substitutions in 5' or 3' flanking DNA.
Hemolymph is a conserved ancestral site of EST6 activity in Drosophila and
the primary sequences regulating its activity lie between -171 and -25 bp
relative to the translation initiation site: deletion of these sequences
decrease activity approximately 20-fold. Hemolymph activity is also
modulated by four other DNA regions, three of which lie 5' and one of which
lies 3' of the coding region. Of these, two have positive and two have
negative effects, each of approximately twofold. Esterase6 activity is
present also in two male reproductive tract tissues; the ejaculatory bulb,
which is another ancestral activity site, and the ejaculatory duct, which
is a recently acquired site within the melanogaster species subgroup.
Activities in these tissues are at least in part independently regulated:
activity in the ejaculatory bulb is conferred by sequences between -273 and
-172 bp (threefold decrease when deleted), while activity in the
ejaculatory duct is conferred by more distal sequences between -844 and
-614 bp (fourfold decrease when deleted). The reproductive tract activity
is further modulated by two additional DNA regions, one in 5' DNA (-613 to
-284 bp; threefold decrease when deleted) and the other in 3' DNA (+1860 to
+2731 bp; threefold decrease when deleted) that probably overlaps the
adjacent esteraseP gene. Collating these data with previous studies
suggests that expression of EST6 in the ancestral sites is mainly regulated
by conserved proximal sequences while more variable distal sequences
regulate expression in the acquired ejaculatory duct site.
相似文献
6.
C Möller G Weber MM Dreyfuss 《Journal of industrial microbiology & biotechnology》1996,17(5-6):359-372
Intraspecific variation among 84 isolates of the anamorphic fungusChaunopycnis alba from 26 different geographical locations was analyzed by investigating optimal growth temperatures, differences in the production of secondary metabolites and presence or absence of the cyclosporin synthetase gene. The genetic diversity was assessed using random amplified polymorphic DNA (RAPD). Analysis of these data showed high genetic, metabolic and physiological diversity within this species. Isolates from the Antarctic represented the most homogeneous group withinC. alba and together with isolates from the Arctic these polar strains differed from alpine, temperate and tropical strains by low optimal growth temperatures and by low production of secondary metabolites. Isolates from tropical climes were characterized by high optimal growth temperatures and by the production of comparatively diverse metabolite spectra. Most of the isolates that were similar in the combination of their physiological and metabolic characters were also genetically related. Isolates from different geographical origins did not show many similarities, with the exception of the cyclosporin A-producing isolates, and large diversity could be observed even within a single habitat. This leads us to the suggestion that for pharmaceutical screening programs samples should be collected from a diversity of different geographical and climatic locations. For the selection of strains for screening the RAPD assay seems to be the most powerful tool. It reflected the highest intraspecific diversity and the results corresponded well with the other characteristics. 相似文献
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A covalently bound photoisomerizable agonist. Comparison with reversibly bound agonists at electrophorus electroplaques 总被引:2,自引:2,他引:0 下载免费PDF全文
HA Lester ME Krouse MM Nass NH Wassermann BF Erlanger 《The Journal of general physiology》1980,75(2):207-232
After disulphide bonds are reduced with dithiothreitol, trans-3- (α-bromomethyl)-3’-[α- (trimethylammonium)methyl]azobenzene (trans-QBr) alkylates a sulfhydryl group on receptors. The membrane conductance induced by this “tethered agonist” shares many properties with that induced by reversible agonists. Equilibrium conductance increases as the membrane potential is made more negative; the voltage sensitivity resembles that seen with 50 [mu]M carbachol. Voltage- jump relaxations follow an exponential time-course; the rate constants are about twice as large as those seen with 50 μM carbachol and have the same voltage and temperature sensitivity. With reversible agonists, the rate of channel opening increases with the frequency of agonist-receptor collisions: with tethered trans-Qbr, this rate depends only on intramolecular events. In comparison to the conductance induced by reversible agonists, the QBr-induced conductance is at least 10-fold less sensitive to competitive blockade by tubocurarine and roughly as sensitive to “open-channel blockade” bu QX-222. Light-flash experiments with tethered QBr resemble those with the reversible photoisomerizable agonist, 3,3’,bis-[α-(trimethylammonium)methyl]azobenzene (Bis-Q): the conductance is increased by cis {arrow} trans photoisomerizations and decreased by trans {arrow} cis photoisomerizations. As with Bis-Q, ligh-flash relaxations have the same rate constant as voltage-jump relaxations. Receptors with tethered trans isomer. By comparing the agonist-induced conductance with the cis/tans ratio, we conclude that each channel’s activation is determined by the configuration of a single tethered QBr molecule. The QBr-induced conductance shows slow decreases (time constant, several hundred milliseconds), which can be partially reversed by flashes. The similarities suggest that the same rate-limiting step governs the opening and closing of channels for both reversible and tethered agonists. Therefore, this step is probably not the initial encounter between agonist and receptor molecules. 相似文献
9.
Activation of cytotoxic function in T lymphocytes. 总被引:8,自引:0,他引:8
D Heininger M Touton A K Chakravarty W R Clark 《Journal of immunology (Baltimore, Md. : 1950)》1976,117(6):2175-2180
The requirements for activation of cytotoxic function in mouse T lymphocytes were investigated. Initial generation of cytotoxicity in normal lymphocytes was equal in magnitude with either Con A or specific alloantigen, and in either case required DNA synthesis. Cytotoxic function in MLC-primed cells could also be regenerated by Con A, the magnitude and target specificity of the cytotoxicity thus generated being indistinguishable from that recalled by specific alloantigen. Cytotoxicity could also be regenerated by third party-stimulating cells; however, the cytotoxicity evoked by third party cells was always specific only for target cells of the original stimulating cell H-2 genotype. The data presented suggest that there are a number of ways to activate cytotoxicity in effector T cells, and are most consistent with a model for T cell triggering that minimizes a strict informational function of antigen-receptor interactions. 相似文献
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