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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.
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The production of cells ofNeisseria gonorrhoeae that form type-T4 colonies in cultures started with cells that originally formed only type-T2 colonies was inhibited by calf thymus RNA. Guanosine and uracil were the only nucleic acid constituents that significantly reduced the T2 to T4 shift. Uracil gave the best results in degree of inhibition. It was found that some tritiated uracil was incorporated into the RNA of growing cells ofN. gonorrhoeae but that much more was incorporated into DNA probably after conversion to guanine and adenine. The data show that the shift from T2 to T4 can be progressively inhibited by increasing the concentration of uracil in the growth medium. 相似文献
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Effect of culture conditions on synthesis of L-asparaginase by Escherichia coli A-1. 总被引:2,自引:1,他引:1
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The nutritional requirements and culture conditions affecting biosynthesis of L-asparaginase in a mutant of Escherichia coli HAP designated strain A-1 were studied. Asparaginase activity was increased by the addition of L-glutamic acid, L-glutamine, or commercial-grade monosodium glutamate. The rate of enzyme synthesis was dependent on the interaction between the pH of the culture and the amount of oxygen dissolved in the medium. A critical oxygen transfer rate essential for asparaginase formation was identified, and a fermentation procedure is described in which enzyme synthesis is controlled by aeration rate. Enhancement of L-asparaginase activity by monosodium glutamate was inhibited by the presence of glucose, culture pH, chloramphenicol, and oxygen dissolved in the fermentation medium. 相似文献
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A. Arnaiz-Villena S. Rodriguez de Córdoba F. Vela J. C. Pascual J. Cerveró A. Bootello 《Human genetics》1981,58(3):344-348
Summary Frequencies of recently described HLA-A,-B (antigens or splits) and HLA-C and HLA-DR antigens are studied in a 450 normal Spaniards sample. The linkage disequilibria are also calculated. HLA-DR7 is more frequent than in any other population studied. Aw30-B18 and Aw33-B14 associations are common and specific Spanish, Basque, and Sardinian HLA features. A11-B27 association is found in our Spanish sample and also in Basques.HLA-Bw4,-Bw6 antigens are analyzed by family mating and segregation and also using unrelated individuals. It shows a good fit as a genetic system. HLA-B antigens are included either in Bw4 or Bw6 according to expectations from other Caucasoid population results. The possibility of a common and North African origen (Iberians) for Spaniards, Basques, and Sardinians is discussed on the basis of presently available HLA data. 相似文献
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