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31.
The melanization response of Aedes trivittatus and the black-eyed Liverpool (LVP) and Rocke-feller (RKF) strains of Aedes aegypti against intrathoracically inoculated Brugia pahangi microfilariae (mff) that previously had penetrated LVP, RKF, or A. trivittatus midguts in vitro was assessed at 1, 3, and 5 days postinoculation (PI). LVP and RKF midgut-derived mff almost totally avoided the melanization response and developed normally in LVP strain A. aegypti, and although over 90% of these mff died by 5 days PI in RKF mosquitoes, the majority of these were not melanized. A. aegypti midgut-derived mff also were able to avoid the response of A. trivittatus in 33–43% of the cases. Penetration through A. trivittatus midguts, however, did not significantly affect the ability of mff to avoid the melanization response in any of the mosquitoes examined. Allogeneic and xenogeneic tissue inplants were accepted by all three mosquito species examined. Data presented support the hypothesis that mff avoid immune recognition in compatible mosquitoes by coating themselves with midgut material(s) during penetration of the midgut in their migration to the hemocoel. 相似文献
32.
Roshan B. Christensen J. R. Christensen Ian Koenig Christopher W. Lawrence 《Molecular & general genetics : MGG》1985,201(1):30-34
Summary Using a nonselective method, we have estimated the proportion of untargeted mutations in the lacI gene of E. coli by transferring either irradiated or unirradiated F pro lac plasmids from an excision deficient donor to an excision deficient pro lac deleted recipient that had been irradiated and allowed to induce recA dependent functions for 30 min. We find that about 10 percent of the mutations induced by either 3.5 Jm-2 or 7 Jm-2 UV are untargeted. 相似文献
33.
Christopher W. Lawrence Beth R. Krauss Roshan B. Christensen 《Mutation research》1985,150(1-2):211-216
Previously isolated mutations in baker's yeast, Saccharomyces cerevisiae, that impair induced mutagenesis were all identified with the aid of tests that either exclusively or predominantly detect base-pair substitutions. To avoid this bias, we have screened 11 366 potentially mutant clones for UV-induced reversion of the frameshift allele, his4–38, and have identified 10 mutants that give much reduced yields of revertants. Complementation and recombination tests show that 6 of these carry mutations at the previously known REV1, REV1 and REV3 loci, while the remaining 4 define 3 new genes, REV4 (2 mutations), REV5 and REV6. The rev4 mutations are readily suppressed in many genetic backgrounds and, like the rev5 mutation, impart only a limited deficiency for induced mutagenesis: it is likely, therefore that the REV4+ and REV5+ gene functions are only remotely concerned with this process. The rev6 mutants have a more general deficiency, however, as well as marked sensitivity to UV and an increased spontaneous mutation rate, properties that suggest the REV6 gene is directly involved in mutation induction. The REV5 gene is located about 1 cM proximal to CYC1 on chromosome X. 相似文献
34.
Identity of the photoproduct that causes lacI mutations in UV-irradiated Escherichia coli. 总被引:7,自引:1,他引:6
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Estimates of the capacity of photoreactivation to act specifically on premutational lesions were obtained by conjugational transfer of an F' lac plasmid from a UV-irradiated, photoreactivated donor to a delta (pro-lac) recipient that had been UV irradiated and allowed to induce SOS functions for 30 min. This treatment reduced the frequency of induced lacI mutations by 70 to 80%, indicating that cyclobutane dimers cause most mutations in this system. 相似文献
35.
Na+-dependent transport of basic, zwitterionic, and bicyclic amino acids by a broad-scope system in mouse blastocysts 总被引:3,自引:0,他引:3
L J Van Winkle H N Christensen A L Campione 《The Journal of biological chemistry》1985,260(22):12118-12123
Mouse blastocysts which had been activated from diapause in utero appeared to take up amino acids via a Na+-dependent transport system with novel characteristics. In contrast to other cell types, uptake of 3-aminoendobicyclo [3,2,1]octane-3-carboxylic acid (BCO) by blastocysts was largely Na+ dependent. Moreover, L-alanine and BCO met standard criteria for mutual competitive inhibition of the Na+-dependent transport of each other. The Ki for each of these amino acids as an inhibitor of transport of the other had a value similar to the value of its Km for transport. In addition, both 2-aminoendobicyclo [2,2,1]heptane-2-carboxylic acid (Ki approximately 1.0 mM) and L-valine (Ki approximately 0.10 mM) appeared to inhibit Na+-dependent transport of alanine and BCO competitively. Finally, alanine and L-lysine appeared to compete for the same Na+-dependent transport sites in blastocysts. For these reasons, we conclude that lysine, alanine, and BCO are transported by a common Na+-dependent system in blastocysts. In addition, the apparent interaction of the system with other basic amino acids, such as 1-dimethylpiperidine-4-amino-4-carboxylic acid, which has a nondissociable positive charge on its side chain, and L-arginine and L-homoarginine, whose cationic forms are highly predominant at neutral pH, suggests that the cationic forms of basic amino acids are transported by the wide-scope system. 相似文献
36.
37.
Bent Christensen 《Hydrobiologia》1984,115(1):91-95
A great variety of asexual reproductive modes are known among aquatic oligochaetes. The main types of these modes are shortly described. Based upon observations on natural populations, the possible genetical and ecological implications of asexual reproduction are discussed. The following points are emphasized: (1) The often expressed expectations of a strong predominance of one particularly adaptive genotype is not born out. (2) In most cases, a number of genetically distinct clones are present in each population, and they show a strong differential distribution in heterogeneous environments, indicating an effective exploitation of the available resources. (3) Most cases of asexual propagation are reproductive strategies of their own and not escape mechanisms. (4) The mechanisms underlying asexual propagation are complex and involve many aspects of the life history. The great variety of types among aquatic oligochaetes offer particularly useful models for the study of these problems. 相似文献
38.
Organic ion transport during seven decades. The amino acids 总被引:17,自引:0,他引:17
H N Christensen 《Biochimica et biophysica acta》1984,779(3):255-269
The amino acids are ions of various charge combinations, and one can argue that historically they were the first ions for which the ongoing problem of membrane transport was presented; also that among transported ions these may undergo a highly detailed molecular recognition. Furthermore, the distribution of charge on the amino acid molecule determines by what route or routes it is conducted across the biological membrane, with what directional and structural specificity, and therefore what regulation is imposed, and where. Cases where a presumably charged chemical group behaves as if it were somehow absent from the amino acid have been observed to fall into several categories: Straightforward cases where the pH has been low enough or high enough to remove the charge by protonation or deprotonation, even in free solution. Cases where that protonation or deprotonation is facilitated at the binding site, and perhaps by the total transport process. The cystine molecule can apparently thus be rendered either a tripolar anion or a tripolar cation for transport. Cases where an otherwise co-transported Na+ is omitted to redress charge, or where a Na+ serves as a surrogate for a missing charged group on the amino acid molecule. A case where the protonation occurs reversibly at the receptor site rather than on the amino acid molecule. 相似文献
39.
Experiments were designed to study the effect of Trypanosoma brucei on the expulsion of Echinostoma revolutum and on the development and maintenance of homologous E. revolutum resistance in the mouse. T. brucei given 3, 2, and 1 wk before and 1 wk after infection with E. revolutum completely inhibited the expulsion of the E. revolutum worm burden for a period of at least 6 wk following infection, and T. brucei given 2 or 3 wk after infection with E. revolutum conferred a significant delay in the expulsion of the E. revolutum worm burden. T. brucei given 1 wk before and 1 wk after a primary E. revolutum infection blocked completely the resistance of the mouse to a homologous E. revolutum challenge given 2 wk after the primary infection. A similar blockage of resistance to a homologous challenge was experienced by mice given T. brucei 3 wk after the primary E. revolutum infection and challenged following another 2 wk. The mechanisms underlying the T. brucei-induced interference with the expulsion of E. revolutum and with the development and maintenance of homologous E. revolutum resistance in mice are presumably immunologically mediated. 相似文献
40.
In order to study carbohydrate-induced protein stabilization bovine testis beta-galactosidase and human serum albumin were conjugated with dextran, partially acetylated dextran and partially methylated dextran. The conjugates and the free proteins were compared with respect to thermal stability at 50 degrees C and resistance to proteolytic digestion by subtilopeptidase A. Both beta-galactosidase and serum albumin were stabilized by conjugation with polysaccharide. However, higher stability was achieved by conjugating the proteins with the hydrophilic polysaccharides, dextran and acetylated dextran, than by conjugation with the hydrophobic polysaccharide, methylated dextran. The results are discussed in relation to possible explanations of carbohydrate-induced protein stabilization. 相似文献