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921.
An exception to the generally conservative nature of plastid gene evolution
is the gene coding for the beta" subunit of RNA polymerase, rpoC2. Previous
work by others has shown that maize and rice have an insertion in the
coding region of rpoC2, relative to spinach and tobacco. To assess the
distribution of this extra coding sequence, we surveyed a broad
phylogenetic sample comprising 55 species from 17 angiosperm families by
using Southern hybridization. The extra coding sequence is restricted to
the grasses (Poaceae). DNA sequence analysis of 11 species from all five
subfamilies within the grass family demonstrates that the extra sequence in
the coding region of rpoC2 is a repetitive array that exhibits more than a
twofold increase in nucleotide substitution, as well as a large number of
insertion/deletion events, relative to the adjacent flanking sequences. The
structure of the array suggests that slipped-strand mispairing causes the
repeated motifs and adds to the mechanisms through which the coding
sequence of plastid genes are known to evolve. Phylogenetic analyses based
on the sequence data from grass species support several relationships
previously suggested by morphological work, but they are ambiguous about
broad relationships within the family.
相似文献
922.
Electron Microscopic Evidence for Linear Insertion of Bacteriophage MU-1 in Lysogenic Bacteria 总被引:16,自引:5,他引:16 下载免费PDF全文
J. Martuscelli A. L. Taylor D. J. Cummings V. A. Chapman S. S. DeLong L. Ca?edo 《Journal of virology》1971,8(4):551-563
Temperate bacteriophage Mu-1 was used to generate a lysogenic derivative of the F'lac episome of Escherichia coli. Intact, covalently circular molecules of F'lac and lysogenic F'lac Mu(+) deoxyribonucleic acid (DNA) were isolated and examined by electron microscopy. The mean contour lengths of F'lac and F'lac Mu(+) molecules were 37.6 +/- 0.4 mum and 53.2 +/- 0.4 mum, respectively. The mean difference, 15.6 mum, is similar to the mean contour length of 12.9 +/- 0.1 mum obtained for linear DNA molecules released by osmotic shock from mature phage Mu-1 virions. These results provide direct physical evidence that phage Mu-1 integrates by linear insertion of its genome into the DNA of lysogenic host bacteria. Chemical and physical analyses of phage Mu-1 DNA indicate that it is similar to E. coli DNA in respect of gross base composition, buoyant density, and melting temperature. 相似文献
923.
Beneficial effects and mechanism of action of Momordica charantia juice in the treatment of streptozotocin-induced diabetes mellitus in rat 总被引:1,自引:0,他引:1
Ahmed I. Adeghate E. Cummings E. Sharma A.K. Singh J. 《Molecular and cellular biochemistry》2004,261(1):63-70
This study investigated the beneficial effects and mechanism of action of the juice of Momordica charantia in streptozotocin (STZ)-induced diabetes mellitus in rats. Diabetes mellitus was associated with significant (p < 0.01) time course reductions in body weight, plasma insulin and the number of insulin positive cells per islet and significant (p < 0.01) time course elevation in blood glucose and osmolarity and systolic blood pressure compared to age-matched healthy controls. Oral intake of M. charantia juice by STZ-induced diabetic rats partially reversed all the diabetes-induced effects measured. Daily oral administration of M. charantia juice to STZ-induced diabetic rates significantly (p < 0.01) reduced the Na+- and K+ -dependent absorptions of glucose by the brush border membrane vesicles of the jejunum compared to the responses obtained in STZ-induced diabetic rat. Either insulin (100 MM) or the fruit juice lyophilised extract (5 g · ml–1) can stimulate 14C-D-glucose uptake in L6 myotubes. These effects were completely blocked by wortmannin, an inhibitor of phosphatidylinositol 3-kinase. High concentrations (10–200 g · ml-1) of M. charantia juice extract inhibited 14C-D-glucose uptake in L6 myotubes compared to the control response. The effect of M. charantia treatment was also investigated on myelinated fibre abnormalities in the tibial nerve of STZ-induced diabetic and control rats. The results show that diabetes was associated with significant (p < 0.05) reduction in the mean cross-sectional myelinated nerve fibres, axonal area, myelin area and maximal fibre area compared to end controls. Treatment of STZ-induced diabetic rats with M. charantia juice normalised the structural abnormalities of peripheral nerves. The results indicate that M. charantia can exert marked beneficial effects in diabetic rats, and moreover, it can regulate glucose uptake into jejunum membrane brush border vesicles and stimulate glucose uptake into skeletal muscle cells similar to the response obtained with insulin. (Mol Cell Biochem 261: 63–70, 2004) 相似文献
924.
The objective of this study was to assess freshwater mussel (Mollusca: Bivalvia: Unionoida) species distributions among the
freshwater ecoregions of Africa and Madagascar to discover areas of high richness and endemism. These are among the top criteria
for identifying biodiversity hotspots and establishing conservation priorities. Distributions were determined from museum
specimens in 17 collections. In total, 5,612 records for 87 unionoid species could each be assigned to one of 90 freshwater
ecoregions. The majority of species (55%) are known from only one (34 spp.) or two (14) ecoregions. Only three are known from
more than 20 ecoregions: Etheria elliptica (38 ecoregions), Chambardia wahlbergi (25), and Mutela rostrata (21). The most species-rich ecoregions are Lake Victoria Basin (17 spp.), Upper Nile (16), Upper Congo (14), Senegal–Gambia
(13), and Sudanic Congo–Oubangi (13). Those with the most endemic species are Lake Tanganyika (8 spp.), Lake Victoria Basin
(6), Bangweulu–Mweru (4), and Lake Malawi (3). Twenty-five ecoregions have no known freshwater mussels. These patterns are
significantly correlated with fish and general freshwater mollusk richness. Unionoid richness also varies significantly among
major habitat types. These patterns are relevant to biogeography and conservation and indicate areas in need of further research.
We argue that freshwater mussels are valuable as focal species for conservation assessments, and they themselves merit management
consideration for their ecosystem functions and distributions in imperiled habitats. It is recommended that field surveys
be conducted to determine the current status of species in all areas of Africa and Madagascar. 相似文献
925.
Colonic contents were obtained from two human sudden-death victims within 3 h of death. One of the subjects (1) was methanogenic, the other (2) was a non-CH4 producer. Measurements of bacterial fermentation products showed that in both individuals short-chain fatty acids, lactate and ethanol concentrations were highest in the caecum and ascending colon. In contrast, products of protein fermentation, such as ammonia, branched chain fatty acids and phenolic compounds, progressively increased from the right to the left colon, as did the pH of gut contents. In Subject 1, cell population densities of methanogenic bacteria (MB) increased distally through the gut and methanogenic activity was lower in the right (0.78-1.18 mumol CH4 produced/h/g dry wt contents) than in the left colon (1.34 mumol CH4 produced/h/g dry wt contents). Methane production rates did not correlate with MB numbers. Sulphate-reducing bacteria (SRB) were not found and dissimilatory sulphate reduction was not detected in any region of the colon. Methanogenic bacteria did not occur in subject 2, but high numbers of SRB were present throughout the gut (ca 10(9)/g dry wt contents). Sulphate reduction rates were maximal in the ascending and transverse colons (0.24 and 0.22 mumol 35SO4(2-) reduced/h/g dry wt contents, respectively). Short-chain fatty acid production by caecal contents was up to eight-fold higher than contents from the sigmoid/rectum. These findings demonstrate significant differences in fermentation reactions in different regions of the large gut. 相似文献
926.
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929.
B Bagar E C Cummings A Mayerová 《Journal of hygiene, epidemiology, microbiology, and immunology》1979,23(2):135-145
Epidemiological features of the epidemic of acute haemorrhagic conjunctivitis in Freetown, Sierra Leone, in 1970, are described. On the basis of hospital figures and a House-to -House survey of 0.9% of the population it is estimated that 50-53% of Freetown's population suffered from the conjunctivitis in 20 weeks. Though no causative agent was isolated, it is supposed, on the basis of the striking similarity with other outbreaks, that the epidemic was caused by enterovirus type 70. Hospital figures, a house-to-house survey and a survey in a closed community provided evidence that man-to-man contact was the principal mode of spread. 相似文献
930.
Since the identification of the gene responsible for HD (Huntington''s
disease), many genetic mouse models have been generated. Each employs a unique
approach for delivery of the mutated gene and has a different CAG repeat length
and background strain. The resultant diversity in the genetic context and
phenotypes of these models has led to extensive debate regarding the relevance
of each model to the human disorder. Here, we compare and contrast the striatal
synaptic phenotypes of two models of HD, namely the YAC128 mouse, which carries
the full-length huntingtin gene on a yeast artificial chromosome, and the CAG140
KI (knock-in) mouse, which carries a human/mouse chimaeric gene that is
expressed in the context of the mouse genome, with our previously published data
obtained from the R6/2 mouse, which is transgenic for exon 1 mutant huntingtin.
We show that striatal MSNs (medium-sized spiny neurons) in YAC128 and CAG140 KI
mice have similar electrophysiological phenotypes to that of the R6/2 mouse.
These include a progressive increase in membrane input resistance, a reduction
in membrane capacitance, a lower frequency of spontaneous excitatory
postsynaptic currents and a greater frequency of spontaneous inhibitory
postsynaptic currents in a subpopulation of striatal neurons. Thus, despite
differences in the context of the inserted gene between these three models of
HD, the primary electrophysiological changes observed in striatal MSNs are
consistent. The outcomes suggest that the changes are due to the expression of
mutant huntingtin and such alterations can be extended to the human
condition. 相似文献