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991.
The phylogenetic position of the archaebacteria and the place of eukaryotes
in the history of life remain a question of debate. Recent studies based on
some protein-sequence data have obtained unusual phylogenies for these
organisms. We therefore collected the protein sequences that were available
with representatives from each of the major forms of life: the
gram-negative bacteria, gram-positive bacteria, archaebacteria, and
eukaryotes. Monophyletic, unrooted phylogenies based on these sequence data
show that seven of 24 proteins yield a significant
gram-positive-archaebacteria clade/gram-negative- eukaryotic clade. The
phylogenies for these seven proteins cannot be explained by the traditional
three-way split of the eukaryotes, archaebacteria, and eubacteria. Nine of
the 24 proteins yield the traditional gram-positive-gram-negative
clade/archaebacteria-eukaryotic clade. The remaining eight proteins give
phylogenies that cannot be statistically distinguished. These results
support the hypothesis of a chimeric origin for the eukaryotic cell nucleus
formed from the fusion of an archaebacteria and a gram-negative bacteria.
相似文献
992.
Phylogenetic analysis of the 90 kD heat shock family of protein sequences and an examination of the relationship among animals, plants, and fungi species 总被引:17,自引:1,他引:16
The heat shock protein (Hsp) sequences, because of their ubiquity and high
degree of conservation, provide useful models for phylogenetic analysis. In
this paper I have carried out a global alignment of all available sequences
(a total of 31) for the 90-kD heat shock protein (Hsp90) family. The
minimum amino acid identity that is seen between presently known Hsp90
homologs is about 40% over the entire length, indicating that it is a
highly conserved protein. Based on the alignment, a number of signature
sequences that either are distinctive of the Hsp90 family or that
distinguish between the cytosolic and the endoplasmic reticular forms of
Hsp90 have been identified. Detailed phylogenetic analyses based on Hsp90
sequences reported here strongly indicate that the cytosolic and the
endoplasmic reticulum (ER) resident forms of Hsp90 constitute paralogous
gene families which arose by a gene duplication event that took place very
early in the evolution of eukaryotic cells. A minimum of two additional
gene duplication events, which took place at a later time, are required to
explain the presence of two different forms of Hsp90 that are found in
fungi and vertebrate species. In a consensus neighbor-joining bootstrap
tree based on Hsp90 sequences, plants and animals species grouped together
989 times of 1,000 (a highly significant score), indicating a closer
relationship between them as compared to fungi. A closer affiliation of
plant and animal species was also observed in the maximum-parsimony tree,
although the relationship was not significantly supported by this method. A
survey of the recent literature on this subject indicates that depending on
the protein sequence and the methods of phylogenetic analysis, the animal
species are indicated as closer relatives to either plants or fungi with
significant statistical support for both topologies. Thus the relationship
among the animal, plant, and fungi kingdoms remains an unresolved issue at
the present time.
相似文献
993.
Crotalaria foliosa Benth. is found to be a later homonym and the new nameCrotalaria mohlenbrockii is proposed to replace it. A new speciesCrotalaria paraguayensis is described andC. martiana Benth. is redefined. 相似文献
994.
995.
996.
Exoerythrocytic (EE) schizonts of Plasmodium fragile were found in liver tissue acquired 7, 8, 9, and 10 days following inoculation of Macaca mulatta monkeys with sporozoites from Anopheles balabacensis balabacensis mosquitoes. There was little to distinguish the EE bodies of P. fragile from EE bodies of many of the other species of primate malaria. 相似文献
997.
W E Collins W Chin M Warren A Y Huong G M Jeffery J C Skinner 《The Journal of parasitology》1982,68(4):657-667
Two strains of Plasmodium falciparum originating in Haiti were studied in the Aotus monkey. The Haitian I/CDC strain was first adapted to in vitro cultivation and subsequently inoculated into monkeys. The Haitian III/CDC strain was inoculated directly from a human patient into the Aotus monkey. The strains varied in their levels of pathogenicity to the animals. The Haitian I/CDC strain was highly virulent in six splenectomized animals; in one intact animal, the infection could be controlled but not eliminated with periodic doses of quinine and chloroquine. After subsequent splenectomy, the animal developed high parasitemias and died. No gametocytes developed in any of the Haitian I infections. The Haitian III strain was lethal to five of the 14 splenectomized monkeys inoculated, but some were able to control their infections without drug intervention. Gametocytes developed in all infections that persisted for an adequate length of time, and infections of mosquitoes were obtained both during the primary attack and the first recrudescence of the parasitemia. Of the mosquitoes tested, Anopheles freeborni was most susceptible to infection, followed by An. culicifacies, An. dirus, An. maculatus, and An. albimanus. The Haitian III strain was successfully transmitted to four other splenectomized Aotus monkeys via sporozoite inoculation using An. freeborni. 相似文献
998.
Summary The improved growth of pine plantations on pasture soils compared with that on soils which previously supported native eucalypt forest is primarily explained in terms of soil phosphorus. Pasture development has resulted in a decrease in the P adsorption maximum of about 300 g g–1 soil, a figure which agrees with the increase in total P due to the application of superphosphate. P adsorption isotherms were used to calculate additions of P to give comparable levels of soil solution P in eucalypt and pasture soils. The growth of pine seedlings in soils thus amended showed a strong N×P interaction. When P was non-limiting, addition of N raised productivity of the eucalypt soil above that of the pasture soil. It is postulated that the different nature of the N×P interaction in eucalypt and pasture soils results from differences in the nitrogen cycle in the two soils. 相似文献
999.
Bone resorption and prostaglandin production by mouse calvaria in vitro: response to exogenous prostaglandins and their precursor fatty acids 总被引:2,自引:0,他引:2
Mouse calvaria were maintained in organ culture for 96 h and endogenous prostaglandin production and active bone resorption (45Ca release) measured. After a lag phase of 12 h, active resorption increased over the 96 h period. The amounts of prostaglandins released into the culture medium (measured by radioimmunoassay) were highest in the first 24 h of culture. Unless these were removed by preculturing for 24 h, or suppressed by indomethacin, no response to exogenous PGE2, or prostaglandin precursors could be demonstrated. Bone resorption was stimulated after preculture by both PGE2 and PGF2 alpha in a dose-dependent manner (10-8M-10-5M), with PGE2 being the more potent. Collagen synthesis was unaffected by PGF2 alpha, whereas PGE2 (10-5M) had an inhibitory effect. Eicosatrienoic acid did not stimulate bone resorption at lower concentrations (10-7M-1-5M), but was inhibitory at 10-4M. Arachidonic acid also inhibited resorption at 10-4m, but at lower concentrations (10-7M-10-5M) increased active resorption. This was concomitant with a rise in PGE2 and PGF2 alpha levels, PGE2 production being significantly higher than PGF2 alpha. The effects of PGE2 (10-8M) and PGF2 alpha (10-8M) appeared additive; there was no evidence of synergistic or antagonistic effects when varying ratios of PGE2: PGF2 alpha were employed. 相似文献
1000.
A series of N-nicotinyl- and N-isonicotinyl-N′-(substituted) ureas were synthesized by a condensation of the appropriate amide with various alkyl or aryl isocyanates, and examined as potential antimetabolites of nicotinamide. No significant microbial toxicity was observed; however, several derivatives in the nicotinyl series proved to be toxic to fish, especially N-nicotinyl-N′-hexylurea which possessed a TL50 of 27 μg/ml. The toxicity was reversed by supplements of nicotinamide but not tryptophan, and may be due to the formation of an inactive NAD complex through the mediation of NADase. Evidence for this possibility is presented by the formation in vitro of an N-nicotinyl[7-14C]N′-ethylurea-NAD analog which was characterized through spectral, chemical, and chromatographic studies. 相似文献