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111.
Christian Biémont Cristina Vieira Christine Hoogland Géraldine Cizeron Catherine Lœvenbruck Claude Arnault Jean-Pierre Carante 《Genetica》1997,100(1-3):161-166
To investigate the main forces controlling the containment of transposable elements (TE) in natural populations, we analyzed
the copia, mdg1, and 412 elements in various populations of Drosophila melanogaster and D. simulans. A lower proportion of
insertion sites on the X chromosome in comparison with the autosomes suggests that selection against the detrimental effects
of TE insertions is the major force containing TE copies in populations of Drosophila. This selection effect hypothesis is
strengthened by the absence of the negative correlation between recombination rate and TE copy number along the chromosomes,
which was expected under the alternative ectopic exchange model (selection against the deleterious rearrangements promoted
by recombination between TE insertions). A cline in 412 copy number in relation to latitude was observed among the natural
populations of D. simulans, with very high numbers existing in some local populations (around 60 copies in a sample from Canberra,
Australia). An apparent absence of selection effects in this Canberra sample and a value of transposition rate equal to 1–2
× 10-3 whatever the population and its copy number agree with the idea of recent but temporarily drastic TE movements in local populations.
The high values of transposition rate in D. simulans clearly disfavor the hypothesis that the low amount of transposable elements
in this species could result from a low transposition rate.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
112.
F. Conti T. Parasassi N. Rosato O. Sapora E. Gratton 《Biochimica et Biophysica Acta (BBA)/Molecular Cell Research》1984,805(1):117-122
Changes in membrane properties during the differentiation process in K562 cells have been investigated. A decrease of lectin-induced agglutination has been detected. The agglutination assay revealed to be an early and sensitive test to monitor the induced differentiation of the K562 cells. Naturally occurring fluorescent fatty acids (cis- and trans-parinaric acids) and the recently developed multifrequency phase and modulation technique were used to study cell membrane properties. Changes in fluorescence lifetime and polarization are clearly associated with cell differentiation, suggesting the involvement of the cellular plasma membrane in the differentiation process. 相似文献
113.
114.
115.
Cristina Casals Carmen Acebal Jesús Pérez-Gil Roberto Arche 《Molecular and cellular biochemistry》1984,63(1):13-20
Summary Lysolecithin:lysolecithin acyltranferase is an enzyme which in several previous studies has shown a dual behavior catalyzing two types of reaction, transacylation or hydrolysis, with the same substrate. Both activities have shown to be dependent on several environmental conditions and among them, the presence of lipids.The addition of several classes of lipids activated in all the cases the enzyme, decreasing the hydrolysis/transacylation molar ratio. This effect was higher for PC/PE/Chol mixture than for other lipids assayed. Circular dichroism spectra of the enzyme did not show any change with the addition of lipids, concluding that the effect of lipids was not due to any structural change in the protein. The hypothesis has been made of an influence of lipids on the physical state of the substrate as well as, possibly, on the enzyme-substrate interaction.The significance of these effects on the physiological role of lysolecithin:lysolecithin acyltransferase from soluble fraction of rabbit lung is discussed.Abbreviations Chol
cholesterol
- CMC
critical micellar concentration
- DPPC
dipalmitoylphosphatidylcholine
- FA
fatty acid
- H/T
hydrolysis/transacylation molar ratio
- LPC
lysophosphatidylcholine
- PC
phosphatidylcholine
- PE
phosphatidylethanolamine
- TG
triglyceride
- UV
ultraviolet 相似文献
116.
Ultrastructural changes during encystment and germination of Bdellovibrio sp. 总被引:1,自引:1,他引:0
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Under proper conditions, Bdellovibrio sp. strain W cells develop into bdellocysts in appropriate prey bacteria. After attachment and penetration of the prey cell, the encysting bdellovibrio began to accumulate inclusion material and increase in size, and was surrounded by an outer layer of amorphous electrondense material. The cytoplasm of the encysting cell appeared more electron dense, and nuclear areas appeared more compact. During germination of bdellocysts, the outer wall was uniformly broken down the inclusion material changed shape and affinity for the heavy metal stain, and the nuclear areas expanded. As the outer wall was dissolved, outgrowth began with the elongation of the germinant as it emerged from the prey ghost as an actively motile cell. 相似文献
117.
Olga Vargas María DEL Carmen Doria de Lorenzo María Cristina Saldate F. Orrego 《Journal of neurochemistry》1977,28(1):165-170
The release of [3H]GABA induced by elevated extracellular potassium (K)o, from thin rat brain cortex slices, has been compared with that of [3H]noradrenaline ([3H]NA), released by the same procedures, both from normal slices, and from slices pre-treated with reserpine and nialamide, [3H]NA being predominantly a vesicular component in the former situation, and a soluble substance in the latter one. 46 mM-(K)o released considerably more [3H]NA from normal than from drug-treated slices, while the release of GABA was about two thirds of the latter. When 4min ‘pulses’ of increasing concentrations of potassium were applied, it was observed that the release of GABA and of [3H]NA from drug-treated slices increased in proportion to (K)o, up to 36-46 mM and then declined considerably with higher (K)o. The dependency of potassium-induced release on the concentration of calcium in the medium, indicated that release of [3H]NA from normal slices was proportional to calcium up to 1.5-2 mM, while that of [3H]NA from drug-treated slices increased up to 0.5 mM-Calcium, and then declined with higher concentrations. GABA release also increased up to 0.5 mM-calcium, but no further changes were observed at higher concentrations. The calcium antagonist D-600 inhibited high (K)o-induced release of [3H]NA from normal slices to a greater extent than that of [3H]GABA or of [3H]NA from drug-treated slices. These results, in which elevated (K)o-induced release of [3H]GABA resembles considerably that of soluble NA, but differs from that of NA present in synaptic vesicles, suggest that release of [3H]GABA also occurs from the soluble cytoplasmic compartment, and that the partial calcium requirement that is found is unrelated to that of transmitter secretion. These findings are also a further indication of the lack of specificity of elevated (K)o as a stimulus for inducing transmitter secretions. 相似文献
118.
A.L. Kovacs E. Brosio F. Conti A. Di Nola G. Napolitano 《Chemistry and physics of lipids》1980,27(2):113-126
A partition energy method procedure was applied to select the energetically favoured conformations of phosphatidylethanolamine (PE) as polar constituents of phospholipid molecules. The result indicated a large degree of freedom for the two torsion angles of the ester bond of the phosphate and a gauche, gauche star conformation for the ethane bond.A packing process of the molecule was carried out through a potential energy calculation by considering the conformers selected above, using previously published procedure and conventions. All the arrangements which possess the best packing energy values were characterised by an orientation of the PN dipolar segment parallel to the lattice plain. Rotation of the internal torsion angles and rotation in the eulerian space of the molecule produced differences in the charged groups that interact. An additional minimum was present in the energy packing process of those conformers which have the first torsion angle of the phosphate in a trans conformation. This minimum, which corresponds to an orientation of the molecule orthogonal to the lattice plane, requires a complete neutralisation of the point charges on the system.The results of the calculation underline the importance of changes in the behaviour of the polar group of the phospholipids in the packing process. 相似文献
119.
R Benigni M Bignami A Carere G Conti L Conti R Crebelli E Dogliotti G Gualandi A Novelletto V A Ortali 《Mutation research》1979,68(3):183-193
Diquat and paraquat were assayed in the following tests. (1) Ames test in Salmonella typhimurium (strains TA1535, TA1537, TA1538, TA98 and TA100) with and without rat-liver microsomal fractions. (2) Resistance to 8-azaguanine in Salmonella typhimurium (strain hisG46, TA92 and TA1535. (3) Repair test in Salmonella typhimurium (strains TA1538 and TA1978). (4) Gene mutations in Aspergillus nidulans: 8-AG resistance and methionine suppression (meth A1 locus). (5) Lethal recessive damage in Aspergillus nidulans. (6) Unscheduled DNA synthesis (UDS) in human epithelial-like cells (EUE). Diquat and paraquat were positive in S. typhimurium (in the repair test and the 8-AG resistance system), in A. nidulans (for gene mutations and lethal recessive damage induction) and in EUE cells (UDS induction). 相似文献
120.
Summary A 2-year-old girl had a de novo duplication in the long arm of one chromosome 7 and an increased level of the enzyme -glucuronidase in cultured fibroblasts. The phenotype of the girl partly overlaps those of two presumptive syndromes due to secondary partial trisomies 7q. The ratio of the enzyme activity was 1.43 to the controls, and 1.37 to her parent's values. We could not define the abnormality but suggest two alternatives: either the patient is trisomic for region q112 to q22 or for the region q22 to q34. If the second alternative is correct the locus for -glucuronidase is possibly assigned to band 7q22. 相似文献