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141.
142.
Two novel gene orders and the role of light-strand replication in rearrangement of the vertebrate mitochondrial genome 总被引:22,自引:8,他引:14
Macey JR; Larson A; Ananjeva NB; Fang Z; Papenfuss TJ 《Molecular biology and evolution》1997,14(1):91-104
Two novel mitochondrial gene arrangements are identified in an agamid
lizard and a ranid frog. Statistical tests incorporating phylogeny indicate
a link between novel vertebrate mitochondrial gene orders and movement of
the origin of light-strand replication. A mechanism involving errors in
light-strand replication and tandem duplication of genes is proposed for
rearrangement of vertebrate mitochondrial genes. A second mechanism
involving small direct repeats also is identified. These mechanisms
implicate gene order as a reliable phylogenetic character. Shifts in gene
order define major lineages without evidence of parallelism or reversal.
The loss of the origin of light-strand replication from its typical
vertebrate position evolves in parallel and, therefore, is a less reliable
phylogenetic character. Gene junctions also evolve in parallel. Sequencing
across multigenic regions, in particular transfer RNA genes, should be a
major focus of future systematic studies to locate novel gene orders and to
provide a better understanding of the evolution of the vertebrate
mitochondrial genome.
相似文献
143.
Evolutionary relationships among the male and female mitochondrial DNA lineages in the Mytilus edulis species complex 总被引:1,自引:0,他引:1
A novel form of mitochondrial DNA (mtDNA) inheritance has previously been
documented for the blue mussel (Mytilus edulis). Female mussels inherit
their mtDNA solely from their mother while males inherit mtDNA from both
their mother and their father. In males, the paternal mtDNA is
preferentially amplified so that the male gonad is highly enriched for the
paternal mtDNA that is then transmitted from fathers to sons. We
demonstrate that this mode of mtDNA inheritance also operates in the
closely related species M. galloprovincialis and M. trossulus. The
evolutionary relationship between the male and female mtDNA lineages is
estimated by phylogenetic analysis of 455 nucleotides from the large
subunit ribosomal RNA gene. We have found that the male and female lineages
are highly divergent; the divergence of these lineages began prior to the
speciation of the three species of blue mussels. Further, the separation
between the male and female lineages is estimated to have occurred between
5.3 and 5.7 MYA.
相似文献
144.
The inhibition of guinea-pig heart (Na+ + K+)-ATPase (ATP phosphohydrolase EC 3.6.1.3) by calcium has been studied at pH 7.4, 6.8 and 6.4. 1. A decrease in pH reduced the threshold inhibitory concentration of calcium and the calcium concentration producing an inhibition of 50% of the enzyme activity. 2. Calcium reduced the apparent affinity of the enzyme of Na+, this effect occurred only at pH 7.4. 3. Calcium increased the apparent affinity of the enzyme for K+, this effect was enhanced at acidic pH. 4. Activation of the enzyme by Na+ for a constant Na+ : K+ ratio has been studied at pH 7.4 and at pH 6.8 in the absence and in the presence of 3.10(-4) M Ca 2+; the results of this experiment indicate that Ca2+ effect at pH 7.4 was not influenced by Na+ -- K+ competition and was probably due to a Na+ -- Ca2+ interaction. 5. At pH 7.4, the calcium inhibitory threshold concentration and the concentration producing 50% inhibition were reduced when Na+ was low; at pH 6.8, the calcium inhibition was not markedly modified by the change of Na+ concentration. 6. The Ca2+ -activated ATPase of myosin B which is related to the contractile behaviour of muscle and the Ca2+ -ATPase of the sarcoplasmic reticulum which is related to the ability of this structure to accumulate calcium were activated in a range of calcium concentration producing an inhibition of (Na2+ + K+) -ATPase. The present results indicate that the increase by acidity of the (Na2+ + K+) -ATPase sensitivity to calcium might be due to a suppression of a Na+ -Ca2+ interaction. On the basis of these observations, it is proposed that calcium might inhibit the Na+ -pump during the repolarization phase of the action potential and that, by this effect, it might control cell excitability. 相似文献
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Summary . Many longitudinal studies generate both the time to some event of interest and repeated measures data. This article is motivated by a study on patients with a renal allograft, in which interest lies in the association between longitudinal proteinuria (a dichotomous variable) measurements and the time to renal graft failure. An interesting feature of the sample at hand is that nearly half of the patients were never tested positive for proteinuria (≥1g/day) during follow-up, which introduces a degenerate part in the random-effects density for the longitudinal process. In this article we propose a two-part shared parameter model framework that effectively takes this feature into account, and we investigate sensitivity to the various dependence structures used to describe the association between the longitudinal measurements of proteinuria and the time to renal graft failure. 相似文献
150.
Thijs H Molenberghs G Michiels B Verbeke G Curran D 《Biostatistics (Oxford, England)》2002,3(2):245-265
Whereas most models for incomplete longitudinal data are formulated within the selection model framework, pattern-mixture models have gained considerable interest in recent years (Little, 1993, 1994). In this paper, we outline several strategies to fit pattern-mixture models, including the so-called identifying restrictions strategy. Multiple imputation is used to apply this strategy to realistic settings, such as quality-of-life data from a longitudinal study on metastatic breast cancer patients. 相似文献