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1.
A phosphotransferase-dependent aryl-β-glucoside uptake and utilisation system (abg) was isolated from the ruminal Clostridium (“C. longisporum”). The system is composed of three genes, abgG, abgF and abgA, and a number of regulatory regions, including terminator/antiterminator type stem-loop structures preceding the abgG and abgF genes. Similarity analysis of the proteins encoded by these genes indicated that they were responsible for the regulation
of the abg system through antitermination (AbgG), the uptake and phosphorylation of aryl-β-glucosides (AbgF) and the hydrolysis of the
intracellular phosphorylated glycosides (AbgA). Experimental evidence for the functions of AbgF and AbgA was obtained. Although
it was not possible to demonstrate any function for AbgG, a promoter 5′ to the abgG gene was identified which was responsible for expression of the downstream genes. The abg system is remarkably similar to operons from the gram negative Enterobacteriaceae, both in the coding and non-coding regulatory
regions.
Received: 3 April 1997 / Accepted: 8 September 1997 相似文献
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S. C. Thomson 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》1998,353(1375):1595-1606
Speakman and co-workers suggested the diurnal Samoan flying fox, Pteropus samoensis, may be at risk of hyperthermia when flying during the day, particularly at high levels of insolation. We monitored activity of this bat and climate simultaneously at two different sites and four times of year in American Samoa. Flight activity varied significantly with time of day, between days, study sites and seasons. Out of the six data sets collected, the four with the highest mean levels of insolation showed a significant decrease in bat numbers with increasing temperature and sunlight. When each individual activity count was directly compared to the predictions of Speakman and co-workers'' biophysical model, 85 to 95% of bat flight activity was found to be in conditions the model suggested would not pose a risk of hyperthermia. This supports the suggestion that in extreme conditions the animals would not fly as they risked overheating. The 5 to 15% of counts in which animals were seen to fly in conditions the model predicted they should not may be explained by erroneous assumptions underlying the model predictions. 相似文献
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J M Al-Hassan M Afzal M Ali M Thomson T Fatima S Fayad R S Criddle 《Comparative biochemistry and physiology. B, Comparative biochemistry》1986,85(1):41-47
Lipids associated with a threat induced epidermal gel secretion from the catfish, Arius thalassinus, have been analyzed. Phospholipids, neutral lipids and glycolipids are all present and each of these subclasses has been analyzed by thin layer and gas chromatography with a general similarity with membrane lipids being noted. The epidermal gel lipids differed from total liver lipids of the catfish. Fatty acid analysis showed the gel lipid to be rich in the unsaturated fatty acids: oleate (omega 7, C18:1), arachidonate (omega 6, C20:4), and docosahexaenoate (omega 3, C22:6). Some prostaglandins were quantitated in lipid extracts from the epidermal gel. 相似文献
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Effect of chronic ethanol and food deprivation on intestinal villus morphology and brush border membrane content of lipid and marker enzymes 总被引:3,自引:0,他引:3
M Keelan K Walker A B Thomson 《Canadian journal of physiology and pharmacology》1985,63(10):1312-1320
Brush border membranes (BBM) were isolated from the jejunum and ileum of control, ad libitum (CAL); control, food-restricted (CFR); control, weight gain (CWG); and ethanol-fed (EF) rabbits. Jejunal alkaline phosphatase activity was similar among control groups, but higher in CAL than EF animals. Sucrase activity was higher in EF and CWG animals than in CAL and CFR. The alkaline phosphatase/sucrase ratio was lower in EF than control animals. Ileal enzyme marker activity was similar among EF and control animals. Sucrase (S) activity was lower in the ileum than in the jejunum. Jejunal free fatty acid and phospholipid/cholesterol (PL/C) were lower in EF than control animals, whereas ileal lipid content was generally similar among all animal groups. Total phospholipid content was similar between sites, but the cholesterol and free fatty acid content were lower in the ileum than the jejunum. The phospholipid/cholesterol ratio was increased only in the ileum of EF animals. The amount of lecithin was decreased in the jejunal BBM of EF animals resulting in a decreased choline/amine phospholipid ratio as compared with control animals. The ileal phospholipid composition was similar among all groups. A large increase in villus height is observed in the jejunum of EF animals. Villus surface area and mucosal surface area are altered with ethanol feeding and food deprivation. Thus, (i) there is a gradient of S and cholesterol between the BBM of jejunum and ileum; (ii) changes in food intake are associated with changes in the morphology as well as the enzyme marker and lipid content of BBM.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
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Cellular interactions in early C. elegans embryos 总被引:8,自引:0,他引:8
In normal development both the anterior and posterior blastomeres in a 2-cell C. elegans embryo produce some descendants that become muscles. We show that cellular interactions appear to be necessary in order for the anterior blastomere to produce these muscles. The anterior blastomere does not produce any muscle descendants after either the posterior blastomere or one of the daughters of the posterior blastomere is removed from the egg. Moreover, we demonstrate that a daughter of the anterior blastomere that normally does not produce muscles appears capable of generating muscles when interchanged with its sister, a cell that normally does produce muscles. Embryos develop normally after these blastomeres are interchanged, suggesting that cellular interactions play a major role in determining the fates of some cells in early embryogenesis. 相似文献
10.
Blood was obtained from 564 11-yr-old children who had participated since birth in a multidisciplinary health and development
study. Serum zinc concentration did not differ between the boys and the girls (mean±SD: 91=17 μg/100 mL,n=453). Five-6% of serum zinc values were low; although there was a weak correlation with height, none of the boys with low
values were below the 10th percentile for height for this group. Serum copper concentration (112±24 μg/100 mL,n=454) was unrelated to sex, height, weight, body mass index, socioeconomic status (SES), or iron status. Blood selenium concentration
(49±10 ng/mL,n=564) was lower than previously reported for Dunedin children; it was higher in children in the lower SES categories. The
data represent normal values for healthy, 11-yr-old NZ children. 相似文献