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1.
Effect of Naturally Occurring nif Reiterations on Symbiotic Effectiveness in Rhizobium phaseoli 总被引:2,自引:0,他引:2 下载免费PDF全文
David Romero Paul W. Singleton Lorenzo Segovia Enrique Morett B. Ben Bohlool Rafael Palacios Guillermo Dvila 《Applied microbiology》1988,54(3):848-850
Most naturally occurring strains of Rhizobium phaseoli possess reiteration of the nif genes. Three regions contain nitrogenase structural genes in strain CFN42. Two of these regions (a and b) have copies of nifH, nifD, and nifK, whereas the third region (c) contains only nifH. Strains containing mutations in either nif region a or nif region b had significantly diminished symbiotic effectiveness compared with the wild-type strain on the basis of nodule mass, total nitrogenase activity per plant, nitrogenase specific activity, total nitrogen in the shoot, and percentage of nitrogen. A strain containing mutations in both nif region a and nif region b was totally ineffective. These data indicate that both nif region a and nif region b are needed for full symbiotic effectiveness in R. phaseoli. 相似文献
2.
Genetic rearrangements of a Rhizobium phaseoli symbiotic plasmid. 总被引:13,自引:8,他引:5
Different structural changes of the Sym plasmid were found in a Rhizobium phaseoli strain that loses its symbiotic phenotype at a high frequency. These rearrangements affected both nif genes and Tn5 mob insertions in the plasmid, and in some cases they modified the expression of the bacterium's nodulation ability. One of the rearrangements was more frequent in heat-treated cells, but was also found under standard culture conditions; other structural changes appeared to be related to the conjugal transfer of the plasmid. 相似文献
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The phylogeny of Greya Busck (Lepidoptera: Prodoxidae) was inferred from
nucleotide sequence variation across a 765-bp region in the cytochrome
oxidase I and II genes of the mitochondrial genome. Most parsimonious
relationships of 25 haplotypes from 16 Greya species and two outgroup
genera (Tetragma and Prodoxus) showed substantial congruence with the
species relationships indicated by morphological variation. Differences
between mitochondrial and morphological trees were found primarily in the
positions of two species, G. variabilis and G. pectinifera, and in the
branching order of the three major species groups in the genus. Conflicts
between the data sets were examined by comparing levels of homoplasy in
characters supporting alternative hypotheses. The phylogeny of Greya
species suggests that host-plant association at the family level and larval
feeding mode are conservative characters. Transition/transversion ratios
estimated by reconstruction of nucleotide substitutions on the phylogeny
had a range of 2.0-9.3, when different subsets of the phylogeny were used.
The decline of this ratio with the increase in maximum sequence divergence
among taxa indicates that transitions are masked by transversions along
deeper internodes or long branches of the phylogeny. Among transitions,
substitutions of A-->G and T-->C outnumbered their reciprocal
substitutions by 2-6 times, presumably because of the approximately 4:1
(77%) A+T-bias in nucleotide base composition. Of all transversions,
73%-80% were A<-->T substitutions, 85% of which occurred at third
positions of codons; these estimates did not decrease with an increase in
maximum sequence divergence of taxa included in the analysis. The high
frequency of A<-->T substitutions is either a reflection or an
explanation of the 92% A+T bias at third codon positions.
相似文献
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M Garcia-Gonzalez M J Alejandre E Garcia-Peregrin J L Segovia 《Biochemical and biophysical research communications》1984,124(3):677-681
Changes observed as a function of chick age in fatty acid composition of lipids from liver microsomes were considerably small, while the unsaturation index increased throughout postnatal development. Supplementation of the diet with 2% cholesterol from hatching produced a significant decrease in the levels of palmitic acid and a clear increase in those of polyunsaturated fatty acids. Maximum effects were attained on day 19 of treatment. Alterations in the fatty acid composition were more pronounced after short-term (48 h) cholesterol feeding. Administration for 48 h of a standard diet to chicks fed a cholesterol diet for 10 days from hatching restored the levels of fatty acids to those of the controls. However, when cholesterol feeding was prolonged for 24 days from hatching, no effect was found after the same treatment. Suppression of the cholesterol diet for 48 h in animals cholesterol fed for 48 h had no effect in 12-day-old chicks while the change to a standard diet produced a reversion of the effect of cholesterol feeding in 26-day-old animals. 相似文献
10.
Lipid composition of brain myelin from normal and hyperphenylalaninemic chick embryos 总被引:1,自引:0,他引:1
M J Alejandre C Marco H Ramirez J L Segovia E Garcia-Peregrin 《Comparative biochemistry and physiology. B, Comparative biochemistry》1984,77(2):329-332
The influence of hyperphenylalaninemia on the lipid composition of brain myelin has been investigated in 19-day-old chick embryos. CNP-ase activity was used as myelin marker enzyme for myelin isolation. CNP-ase activity was significantly lower in hyperphenylalaninemic myelin when compared with control. No significant differences were observed after experimental treatment in the total lipid content of myelin as well as in the proportion of cholesterol:phospholipid:galactolipid. Nevertheless, a clear increase in the percentage of esterified cholesterol was found. No appreciable alterations were observed in the phospholipid composition of brain myelin from both control and hyperphenylalaninemic chick embryos. However, the ratio of unsaturated to saturated fatty acids in serine plasmalogen and sphingomyelin was considerably increased by this treatment. This ratio in choline and ethanolamine phosphatides from treated embryos did not differ from that of controls. 相似文献