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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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Sílvia Bronsoms Josep Villanueva Francesc Canals Enrique Querol Francesc X Aviles 《European journal of biochemistry》2003,270(17):3641-3650
Protein folding can be modulated in vivo by many factors. While chaperones act as folding catalysts and show broad substrate specificity, some pro-peptides specifically facilitate the folding of the mature protein to which they are bound. Potato carboxypeptidase inhibitor (PCI), a 39-residue protein carboxypeptidase inhibitor, is synthesized in vivo as a precursor protein that includes a 27-residue N-terminal and a seven-residue C-terminal pro-regions. In this work the disulfide-coupled folding of mature PCI in vitro has been compared with that of the same protein extended with either the N-terminal pro-sequence (ProNtPCI) or both N- and C-terminal pro-sequences (ProPCI), and also with the N-terminal pro-sequence in trans (ProNt + PCI). No significant differences can be observed in the folding kinetics or efficiencies of all these molecules. In addition, in vivo folding studies in Escherichia coli have been performed using wild-type PCI and three PCI mutant forms with and without the N-terminal pro-sequence, the mutations had been previously reported to affect folding of the PCI mature form. The extent to which the 'native-like' form was secreted to the media by each construction was not affected by the presence of the N-terminal pro-sequence. These results indicate that PCI does not depend on the N-terminal pro-sequence for its folding in both, in vitro and in vivo in E. coli. However, structural analysis by spectroscopy, hydrogen exchange and limited proteolysis by mass spectrometry, indicate the capability of such N-terminal pro-sequence to fold within the precursor form. 相似文献
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