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21.
Evolution of eutherian cytochrome c oxidase subunit II: heterogeneous rates of protein evolution and altered interaction with cytochrome c 总被引:3,自引:1,他引:2
Cytochrome c oxidase subunit II (COII), encoded by the mitochondrial
genome, exhibits one of the most heterogeneous rates of amino acid
replacement among placental mammals. Moreover, it has been demonstrated
that cytochrome c oxidase has undergone a structural change in higher
primates which has altered its physical interaction with cytochrome c. We
collected a large data set of COII sequences from several orders of mammals
with emphasis on primates, rodents, and artiodactyls. Using phylogenetic
hypotheses based on data independent of the COII gene, we demonstrated that
an increased number of amino acid replacements are concentrated among
higher primates. Incorporating approximate divergence dates derived from
the fossil record, we find that most of the change occurred independently
along the New World monkey lineage and in a rapid burst before apes and Old
World monkeys diverged. There is some evidence that Old World monkeys have
undergone a faster rate of nonsynonymous substitution than have apes. Rates
of substitution at four-fold degenerate sites in primates are relatively
homogeneous, indicating that the rate heterogeneity is restricted to
nondegenerate sites. Excluding the rate acceleration mentioned above,
primates, rodents, and artiodactyls have remarkably similar nonsynonymous
replacement rates. A different pattern is observed for transversions at
four-fold degenerate sites, for which rodents exhibit a higher rate of
replacement than do primates and artiodactyls. Finally, we hypothesize
specific amino acid replacements which may account for much of the
structural difference in cytochrome c oxidase between higher primates and
other mammals.
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22.
Paired sequence difference in ribosomal RNAs: evolutionary and phylogenetic implications 总被引:12,自引:1,他引:11
Ribosomal RNAs have secondary structures that are maintained by internal
Watson-Crick pairing. Through analysis of chordate, arthropod, and plant 5S
ribosomal RNA sequences, we show that Darwinian selection operates on these
nucleotide sequences to maintain functionally important secondary
structure. Insect phylogenies based on nucleotide positions involved in
pairing and the production of secondary structure are incongruent with
those constructed on the basis of positions that are not. Furthermore,
phylogeny reconstruction using these nonpairing bases is concordant with
other, morphological data.
相似文献
23.
Polyomavirus and papillomavirus (papovavirus) capsids are composed of 72 capsomeres of their major capsid proteins, VP1 and L1, respectively. After translation in the cytoplasm, L1 and VP1 pentamerize into capsomeres and are then imported into the nucleus using the cellular α and β karyopherins. Virion assembly only occurs in the nucleus, and cellular mechanisms exist to prevent premature capsid assembly in the cytosol. We have identified the karyopherin family of nuclear import factors as possible “chaperones” in preventing the cytoplasmic assembly of papovavirus capsomeres. Recombinant murine polyomavirus (mPy) VP1 and human papillomavirus type 11 (HPV11) L1 capsomeres bound the karyopherin heterodimer α2β1 in vitro in a nuclear localization signal (NLS)-dependent manner. Because the amino acid sequence comprising the NLS of VP1 and L1 overlaps the previously identified DNA binding domain, we examined the relationship between karyopherin and DNA binding of both mPy VP1 and HPV11 L1. Capsomeres of L1, but not VP1, bound by karyopherin α2β1 or β1 alone were unable to bind DNA. VP1 and L1 capsomeres could bind both karyopherin α2 and DNA simultaneously. Both VP1 and L1 capsomeres bound by karyopherin α2β1 were unable to assemble into capsids, as shown by in vitro assembly reactions. These results support a role for karyopherins as chaperones in the in vivo regulation of viral capsid assembly. 相似文献
24.
25.
Transcription and in vitro processing of yeast 5 S rRNA 总被引:3,自引:0,他引:3
A method is described for the isolation of a yeast chromatin fraction highly enriched in ribosomal DNA sequences. In the presence of exogenous yeast RNA polymerase III, this purified chromatin actively synthesizes a set of 5 S ribosomal RNAs all of which have 5'-sequences identical with mature 5 S RNA but which end with a variable number (up to 10) of additional residues at the 3'-terminus. These extra nucleotides are precisely removed by a processing nuclease found in the chromatin supernatant fraction. 相似文献
26.
27.
Capsomers were produced in bacteria as glutathione-S-transferase (GST) fusion proteins with human papillomavirus type 16 L1 lacking the first nine and final 29 residues (GST-HPV16L1Δ) alone or linked with residues 13–47 of HPV18, HPV31 and HPV45 L2 in tandem (GST-HPV16L1Δ-L2x3). Subcutaneous immunization of mice with GST-HPV16L1Δ or GST-HPV16L1Δ-L2x3 in alum and monophosphoryl lipid A induced similarly high titers of HPV16 neutralizing antibodies. GST-HPV16L1Δ-L2x3 also elicited moderate L2-specific antibody titers. Intravaginal challenge studies showed that immunization of mice with GST-HPV16 L1Δ or GST-HPV16L1Δ-L2x3 capsomers, like Cervarix®, provided complete protection against HPV16. Conversely, vaccination with GST-HPV16 L1Δ capsomers failed to protect against HPV18 challenge, whereas mice immunized with either GST-HPV16L1Δ-L2x3 capsomers or Cervarix® were each completely protected. Thus, while the L2-specific response was moderate, it did not interfere with immunity to L1 in the context of GST-HPV16L1Δ-L2x3 and is sufficient to mediate L2-dependent protection against an experimental vaginal challenge with HPV18. 相似文献
28.
We previously have published data detailing the time course of taste bud regeneration in the anterior tongue following transection of the chorda tympani (CT) nerve in the rat. This study extends the prior work by determining the time course of taste bud regeneration in the vallate papilla, soft palate and nasoincisor ducts (NID) following transection of either the glossopharyngeal (GL) or greater superficial petrosal (GSP) nerve. Following GL transection in rats (n = 6 per time point), taste buds reappeared in the vallate papilla between 15 and 28 days after surgery, and returned to 80.3% of control levels (n = 12) of taste buds by 70 days postsurgery. The first appearance and the final percentage of the normal complement of regenerated vallate taste buds after GL transection resembled that seen previously in the anterior tongue after CT transection. However, in the latter case, regenerated taste buds reached asymptotic levels by 42 days after surgery, whereas within the time frame of the present study, a clear asymptotic return of vallate taste buds was not observed. In contrast to the posterior (and anterior) tongue, only 25% of the normal complement of palatal taste buds regenerated by 112 days and 224 days after GSP transection (n = 9). The difference in regenerative capacity might relate to the surgical approach used to transect the GSP. These experiments provide useful parametric data for investigators studying the functional consequences of gustatory nerve transection and regeneration. 相似文献
29.
Mitochondrial gene order is not conserved in arthropods: prostriate and metastriate tick mitochondrial genomes 总被引:25,自引:15,他引:10
The entire mitochondrial genome was sequenced in a prostriate tick, Ixodes
hexagonus, and a metastriate tick, Rhipicephalus sanguineus. Both genomes
encode 22 tRNAs, 13 proteins, and two ribosomal RNAs. Prostriate ticks are
basal members of Ixodidae and have the same gene order as Limulus
polyphemus. In contrast, in R. sanguineus, a block of genes encoding NADH
dehydrogenase subunit 1 (ND1), tRNA(Leu)(UUR), tRNA(Leu)(CUN), 16S rDNA,
tRNA(Val), 12S rDNA, the control region, and the tRNA(Ile) and tRNA(Gln)
have translocated to a position between the tRNA(Glu) and tRNA(Phe) genes.
The tRNA(Cys) gene has translocated between the control region and the
tRNA(Met) gene, and the tRNA(Leu)(CUN) gene has translocated between the
tRNA(Ser)(UCN) gene and the control region. Furthermore, the control region
is duplicated, and both copies undergo concerted evolution. Primers that
flank these rearrangements confirm that this gene order is conserved in all
metastriate ticks examined. Correspondence analysis of amino acid and codon
use in the two ticks and in nine other arthropod mitochondrial genomes
indicate a strong bias in R. sanguineus towards amino acids encoded by
AT-rich codons.
相似文献
30.
Identification of the threonine phosphorylation sites on the polyomavirus major capsid protein VP1: relationship to the activity of middle T antigen. 总被引:4,自引:1,他引:3 下载免费PDF全文
Phosphorylation of the polyomavirus major capsid protein VP1 was examined after in vivo 32P labeling of virus-infected cells. Two phosphorylated peptide fragments of VP1 were identified by protease digestion, high-performance liquid chromatography purification, mass spectrometry, and N-terminal sequencing. The peptides from residues 58 to 78 and residues 153 to 173 were phosphorylated on threonine. Site-directed mutations were introduced at these threonine sites, and mutant viruses were reconstructed. A threonine-to-glycine change at residue 63 (mutant G63) and a threonine-to-alanine change at residue 156 (mutant A156) resulted in viruses defective in phosphorylation of the respective peptides after in vivo labeling. Growth of the mutant G63 virus was similar to that of the wild-type virus, but the mutant A156 was inefficient in assembly of 240S viral particles. Polyomavirus nontransforming host range (hr-t) mutants are defective in VP1 threonine phosphorylation when grown in nonpermissive cells (R. L. Garcea, K. Ballmer-Hofer, and T. L. Benjamin, J. Virol. 54:311-316, 1985). Proteolytic mapping of VP1 peptides after in vivo labeling from hr-t mutant virus infections demonstrated that both residues T-63 and T-156 were affected. These results suggest that the block in virion assembly in hr-t mutant viruses is associated with a defect in phosphorylation of threonine 156. 相似文献