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101.
Primary cell cultures derived from mutants in seventeen different genes were analyzed for their ability to excise pyrimidine
dimers from DNA. Five of these mutagen-sensitive mutants [mus(2)205A1, mus(3)302D1, mus(3) 304D3, mus(3)306D1, mus(3)308D2] display a significantly reduced excision capacity relative to control cultures. In addition, two of the five [mus(3)306D1, mus(3)308D2] are defective in the accumulation of single-strand breaks normally seen after ultraviolet irradiation. This study, therefore,
brings the total number of Drosophila mutants known to be defective in excision repair to seven. The results are discussed relative to other genetic and biochemical
properties of these mutants.
This work is dedicated to Professor W. Beermann whose own contributions were instrumental in focusing a modern analysis of
the eukaryotic genome on the diptera. Those of us who benefitted so much from his personal guidance recognize that we did
so as a result of some sacrifice on his part. One of Boyd's contemporaries in Tübingen once remarked: “It's terrifying to
think what Professor Beermann could do if he were in the lab full time.” 相似文献
102.
1. The compound trans-1,4 bis-(2-dichlorobenzylaminomethyl)cyclohexane dihydrochloride (AY9944) blocks cholesterol synthesis at a late stage. This leads to a decrease in cholesterol and accumulation of cholesta-5,7-diene-3-beta-ol (7-dehydrocholesterol) in tissues and plasma. 2. The effect of AY9944 on bile salt synthesis in rat liver was studied. The synthesis of conjugated cholic and chenodeoxycholic acids was measured in hepatocytes isolated from rats 2 h, 24 h and 48 h after administration of a single oral dose of AY9944. Production of the two bile salts was inhibited by 70-80% in hepatocytes from AY9944-treated as compared to untreated animals. 3. When AY9944 was added to the incubation medium in vitro of hepatocytes prepared from untreated rats the synthesis of conjugated cholic and chenodeoxycholic acids was not inhibited during the first hour of incubation, probably because of the presence of endogenous cholesterol. However when hepatocytes from untreated rats were incubated with AY9944 for periods of 2 h or longer, bile salt production was decreased markedly. 4. Bile salt synthesis is stimulated when rats are subjected to total biliary drainage for 24 h. The effect of AY9944 on this stimulation was studied. The content of conjugated cholic and chenodeoxycholic acid in the bile was measured as an indicator of bile salt synthesis. 5. In control animals the rate of secretion of biliary bile salts began to increase after about 24 h of total biliary drainage and reached a maximum after approximately 36 h. A single oral dose of AY9944 given 2 h after the start of total biliary drainage delayed and reduced this response. 6. The results show that inhibition of cholesterol synthesis by AY9944 resulting in the replacement of cholesterol by 7-dehydrocholesterol decreases but does not completely prevent bile salt synthesis. 相似文献
103.
Claude E. Boyd 《Hydrobiologia》1981,80(1):91-93
Ion-pairing has little effect on ionic activity calculations for weakly mineralized natural water (ionic strength < 2 mM). However, for more strongly mineralized freshwaters, corrections for ion-pairing are necessary if highly accurate ionic activities are required. 相似文献
104.
Multiple electrophoretic forms of methyl-accepting chemotaxis proteins generated by stimulus-elicited methylation in Escherichia coli. 总被引:21,自引:12,他引:9 下载免费PDF全文
The tsr and tar genetic loci of Escherichia coli determine the presence in sodium dodecyl sulfate-polyacrylamide gel electrophoresis of methyl-accepting chemotaxis proteins (MCPs) I and II, respectively, each of which consists of a distinct group of multiple bands. Synthesis of the tsr and tar products was directed in ultraviolet-irradiated bacteria by lambda transducing phages. The addition of appropriate chemotactic stimuli to these cells resulted in the appearance of additional, faster migrating electrophoretic forms of the Tsr and Tar polypeptides which disappeared upon removal of the stimulus. The stimulus-elicited forms comigrated with component bands of the corresponding MCPs. These results indicate that methylation itself caused shifts in electrophoretic mobility and hence led to the observed MCP band patterns. The number of Tsr species suggested that there were at least three methylated sites on the Tsr polypeptide. The conclusion that methylation generates multiplicity was supported by the results of experiments in which the tsr product was synthesized in mutant bacteria defective in specific chemotaxis functions concerned with methylation or demethylation of MCPs. Thus, the presence of a cheX defect blocked the stimulus-elicited appearance of faster migrating forms of the tsr product; conversely, the presence of a cheB defect resulted in a pronounced shift toward these forms in the absence of a chemotactic stimulus. 相似文献
105.
106.
Fine structural details of the parasitic yeastlike phase of Sporothrix schenckii contained in biopsy tissue from a naturally-occurring case of disseminated feline sporotrichosis are described and illustrated by electron microscopy. Both free and phagocytosed fungal cells were observed. The fungal cells were contained within an extracellular, electron transparent vacuolar area which was bounded by a limiting membrane of probable host origin. The yeastlike cells were characterized by a conspicuous layer of osmiophilic microfilaments which occurred along the outermost surface of the cell wall. In many yeastlike cells, scattered, membranebound vacuoles containing electron opaque material were observed in the cytoplasm. Asteroid bodies were not observed. 相似文献
107.
The specificity of the interaction between the cholesterol side chain and egg phosphatidylcholine was precisely defined by examining the effect of three new analogues of cholesterol with modified side chains on the ordering of two steroid spin labels in liposomes. The complete side chain of cholesterol was shown to be required for maximum ordering. Sterols with side chains shorter or longer than cholesterol caused significantly less ordering. 相似文献
108.
The stoichiometry of calcium-ion chelation to alginate chains has been investigated by circular dichroism (c.d.), and by equilibrium dialysis in the presence of various concentrations of sodium chloride. C.d. intensity in the carboxylate π → π * spectral region increases linearly with calcium-ion concentration up to a level equivalent to half the total poly-L-guluronate stoichiometric requirement, and thereafter shows little further change. Similarly, the level of bound calcium resistant to displacement by swamping concentrations of sodium ions is equivalent to half the stoichiometric requirement of poly-L-guluronate chain-sequences alone. In terms of the previously developed “egg-box” model of co-operative junction-zone formation in alginate gelation, these results are interpreted as showing that the primary mechanism of interchain association is by dimerisation of poly-L-guluronate chain-segments in a regular, buckled, two-fold conformation related to that characterized for the free acid in the solid state, with tight interchain chelation of calcium to the carboxylate groups on the interior faces of the dimer (i.e., half the carboxylate residues of the participating chain-sequences). This interpretation is entirely consistent with previous evidence from electron microscopy, and offers a simple rationalisation of experimental results from competitive-ion binding studies. 相似文献
109.
It is reported that chromatin can be prepared from highly purified polytene nuclei from the salivary glands of third instar larvae of Drosophila hydei; such chromatin differs from that of diploid nuclei mainly by deficiencies in certain nonhistone chromosomal proteins. It is suggested that these proteins are important components of constitutive heterochromatin, which is severely underrepresented in polytene chromosomes. Chromosome morphology, including the pattern of induced puffs, is maintained throughout the mass isolation of glands and sucrose gradient purification of nuclei, as indicated by studies on temperature-shocked and control larvae. No significant alteration in the chromosomal proteins following puff induction by heat shock could be detected on analysis of the isolated protein fractions by disc gel electrophoresis. More sensitive techniques must be developed to study the apparent rearrangement or accumulation of protein at puff sites, and to elucidate the role of this protein in gene activation. 相似文献
110.
M W Pulliam L F Boyd N C Baglan R A Bradshaw 《Biochemical and biophysical research communications》1975,67(4):1281-1289
The binding characteristics of [125I]nerve growth factor, covalently cross-linked with dimethyl suberimidate, to chick embryonic dorsal root ganglia are indistinguishable from the iodinated native hormone. Both show non-saturability, non-linear Scatchard plots and acceleration of dissociation of hormone-receptor complexes by native hormone which is reflected in the binding constants calculated. These results demonstrate that dimerization of the native hormone at the receptor is not responsible for the negatively cooperative behavior observed for native nerve growth factor. Further, experiments with amino-silylated glass tubes also eliminate interaction between hormone and reaction vessel as an explanation of the non-saturable and multiple affinity properties of the observed binding. 相似文献