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1.
A comparative description of mitochondrial DNA differentiation in selected avian and other vertebrate genera 总被引:14,自引:1,他引:13
Levels of mitochondrial DNA (mtDNA) sequence divergence between species
within each of several avian (Anas, Aythya, Dendroica, Melospiza, and
Zonotrichia) and nonavian (Lepomis and Hyla) vertebrate genera were
compared. An analysis of digestion profiles generated by 13-18 restriction
endonucleases indicates little overlap in magnitude of mtDNA divergence for
the avian versus nonavian taxa examined. In 55 interspecific comparisons
among the avian congeners, the fraction of identical fragment lengths (F)
ranged from 0.26 to 0.96 (F = 0.46), and, given certain assumptions, these
translate into estimates of nucleotide sequence divergence (p) ranging from
0.007 to 0.088; in 46 comparisons among the fish and amphibian congeners, F
values ranged from 0.00 to 0.36 (F = 0.09), yielding estimates of P greater
than 0.070. The small mtDNA distances among avian congeners are associated
with protein-electrophoretic distances (D values) less than approximately
0.2, while the mtDNA distances among assayed fish and amphibian congeners
are associated with D values usually greater than 0.4. Since the
conservative pattern of protein differentiation previously reported for
many avian versus nonavian taxa now appears to be paralleled by a
conservative pattern of mtDNA divergence, it seems increasingly likely that
many avian species have shared more recent common ancestors than have their
nonavian taxonomic counterparts. However, estimates of avian divergence
times derived from mtDNA- and protein-calibrated clocks cannot readily be
reconciled with some published dates based on limited fossil remains. If
the earlier paleontological interpretations are valid, then protein and
mtDNA evolution must be somewhat decelerated in birds. The empirical and
conceptual issues raised by these findings are highly analogous to those in
the long-standing debate about rates of molecular evolution and times of
separation of ancestral hominids from African apes.
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The C-terminal proteolytic processing product of merozoite surface protein 1 (MSP1) appears essential for successful erythrocyte invasion by the malarial parasite, Plasmodium. We have determined the crystal structure at 1.8 A resolution of a soluble baculovirus-recombinant form of the protein from P. cynomolgi, which confers excellent protective efficacy in primate vaccination trials. The structure comprises two EGF-like domains, and sequence comparisons strongly suggest that the same conformation is present in all species of Plasmodium, including P. falciparum and P. vivax, which are pathogenic in man. In particular, conserved interdomain contacts between the two EGF modules should preserve the compact form of the molecule in all species. Implications of the crystal structure for anti-malarial vaccine development are discussed. 相似文献
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The viability of Clavibacter michiganensis subsp. michiganensis (Cmm) was determined by measuring the intracellular pH (pHin) as a viability parameter. This was based on the observation that growth of Cmm was inhibited at pH 5.5 and below. Therefore, viable cells should maintain their pHin above this pH value. The pHin of Cmm was determined using the fluorescent probe 5(and 6-)-carboxyfluorescein succinimidyl ester (cFSE). The pHin of Cmm cells exposed to acid treatments was determined using fluorescence spectrofluorometry, and for cells exposed to elevated temperatures, the pHin was determined using fluorescence spectrofluorometry and flow cytometry (FCM). A good correlation was found between the presence of a pH gradient and the number of colony-forming units (cfu) observed in plate counts. However, with the spectrofluorometry technique, the analysis is based on the whole cell population and the detection sensitivity of this technique is rather low, i.e., cell numbers of at least 107 cfu ml-1 are needed for the analysis. Using FCM, heat-treated and non-treated Cmm cells could be distinguished based on the absence and presence of a pH gradient, respectively. The major advantage of FCM is its high sensitivity, allowing analysis of microbial populations even at low numbers, i.e., 102-103 cfu ml-1. 相似文献
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We studied different genetic models and evaluation systems to select against a genetic disease with additive, recessive or polygenic inheritance in genetic conservation schemes. When using optimum contribution selection with a restriction on the rate of inbreeding (ΔF) to select against a disease allele, selection directly on DNA-genotypes is, as expected, the most efficient strategy. Selection for BLUP or segregation analysis breeding value estimates both need 1–2 generations more to halve the frequency of the disease allele, while these methods do not require knowledge of the disease mutation at the DNA level. BLUP and segregation analysis methods were equally efficient when selecting against a disease with single gene or complex polygene inheritance, i.e. knowledge about the mode of inheritance of the disease was not needed for efficient selection against the disease. Smaller schemes or schemes with a more stringent restriction on ΔF needed more generations to halve the frequency of the disease alleles or the fraction of diseased animals. Optimum contribution selection maintained ΔF at its predefined level, even when selection of females was at random. It is argued that in the investigated small conservation schemes with selection against a genetic defect, control of ΔF is very important. 相似文献
6.
Comparisons of the molecular evolutionary process at rbcL and ndhF in the grass family (Poaceae) 总被引:2,自引:1,他引:1
We examine rate heterogeneity among evolutionary lineages of the grass
family at two plasmid loci, ndhF and rbcL, and we introduce a method to
determine whether patterns of rate heterogeneity are correlated between
loci. We show both that rates of synonymous evolution are heterogeneous
among grass lineages and that are heterogeneity is correlated between loci
at synonymous sites. At nonsynonymous sites, the pattern of rate
heterogeneity is not correlated between loci, primarily due to an aberrant
pattern of rate heterogeneity at nonsynonymous sites of rbcL. We compare
patterns of synonymous rate heterogeneity to predictors based on the
generation time effect and the speciation rate hypotheses. Although there
is some evidence for generation time effects, neither generation time
effects nor speciation rates appear to be sufficient to explain patterns of
rate heterogeneity in the grass plastid sequences.
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7.
L. Nerva W. Chitarra I. Siciliano F. Gaiotti M. Ciuffo M. Forgia G. C. Varese M. Turina 《Environmental microbiology》2019,21(6):1957-1968
To date, no demonstration of a direct correlation between the presence of mycoviruses and the quantitative or qualitative modulation of mycotoxins has been shown. In our study, we transfected a virus-free ochratoxin A (OTA)-producing isolate of Aspergillus ochraceus with purified mycoviruses from a different A. ochraceus isolate and from Penicillium aurantiogriseum. Among the mycoviruses tested, only Aspergillus ochraceus virus (AoV), a partitivirus widespread in A. ochraceus, caused a specific interaction that led to an overproduction of OTA, which is regulated by the European Commission and is the second most important contaminant of food and feed commodities. Gene expression analysis failed to reveal a specific viral upregulation of the mRNA of genes considered to play a role in the OTA biosynthetic pathway. Furthermore, AoOTApks1, a polyketide synthase gene considered essential for OTA production, is surprisingly absent in the genome of our OTA-producing isolate. The possible biological and evolutionary implications of the mycoviral regulation of mycotoxin production are discussed. 相似文献
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Job B Bernheim A Beau-Faller M Camilleri-Broët S Girard P Hofman P Mazières J Toujani S Lacroix L Laffaire J Dessen P Fouret P;LG Investigators 《PloS one》2010,5(12):e15145