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61.
62.
Single-copy nuclear DNAs (scnDNAs) of eight species of arvicoline and six
species of murine rodents were compared using DNA-DNA hybridization. The
branching pattern derived from the DNA comparisons is congruent with the
fossil evidence and supported by comparative biochemical, chromosomal, and
morphological studies. The recently improved fossil record for these
lineages provides seven approximate divergence dates, which were used to
calibrate the DNA-hybridization data. The average rate of scnDNA divergence
was estimated as 2.5%/Myr. This is approximately 10 times the rate in the
hominoid primates. These results agree with previous reports of accelerated
DNA evolution in muroid rodents and extend the DNA-DNA hybridization data
set of Brownell.
相似文献
63.
Carbohydrates have been suggested to account for some IgE cross- reactions
between various plant, insect, and mollusk extracts, while some IgG
antibodies have been successfully raised against plant glycoproteins. A rat
monoclonal antibody raised against elderberry abscission tissue (YZ1/2.23)
and rabbit polyclonal antiserum against horseradish peroxidase were
screened for reactivity in enzyme-linked immunosorbent assay against a
range of plant glycoproteins and extracts as well as neoglycoproteins, bee
venom phospholipase, and several animal glycoproteins. Of the
oligosaccharides tested, Man3XylFucGlcNAc2(MMXF3) derived from horseradish
peroxidase was the most potent inhibitor of the reactivity of both YZ1/2.23
and anti- horseradish peroxidase to native horseradish peroxidase
glycoprotein. The reactivity of YZ1/2. 23 and anti-horseradish peroxidase
against Sophora japonica lectin was most inhibited by a neoglycoconjugate
of bromelain glycopeptide cross-linked to bovine serum albumin, while the
defucosylated form of this conjugate was inactive as an inhibitor. A wide
range of plant extracts was found to react against YZ1/2.23 and
anti-horseradish peroxidase, with particularly high reactivities recorded
for grass pollen and nut extracts. All these reactivities were inhibitable
with the bromelain glycopeptide/bovine serum albumin conjugate. Bee venom
phospholipase and whole bee venom reacted weakly with YZ1/2.23 but more
strongly with anti-horseradish peroxidase in a manner inhibitable with the
bromelain glycopeptide/bovine serum albumin conjugate, while hemocyanin
from Helix pomatia reacted poorly with YZ1/2.23 but did react with
anti-horseradish peroxidase. It is concluded that the alpha1, 3-fucose
residue linked to the chitobiose core of plant glycoproteins is the most
important residue in the epitope recognized by the two antibodies studied,
but that the polyclonal anti-horseradish peroxidase antiserum also contains
antibody populations that recognize the xylose linked to the core mannose
of many plant and gastropod N-linked oligosaccharides.
相似文献
64.
Structural comparison of fibroblast growth factor-specific heparan sulfates derived from a growing or differentiating neuroepithelial cell line 总被引:3,自引:1,他引:2
Brickman YG; Nurcombe V; Ford MD; Gallagher JT; Bartlett PF; Turnbull JE 《Glycobiology》1998,8(5):463-471
Heparan sulfate (HS) glycosaminoglycans are essential modulators of
fibroblast growth factor (FGF) activity both in vivo and in vitro, and
appear to act by cross-linking particular forms of FGF to appropriate FGF
receptors. We have recently isolated and characterized two separate HS
pools derived from immortalized embryonic day 10 mouse neuroepithelial 2.3D
cells: one from cells in log growth phase, which greatly potentiates the
activity of FGF-2, and the other from cells undergoing contact-inhibition
and differentiation, which preferentially activates FGF-1. These two pools
of HS have very similar functional activities to those species isolated
from primary neuroepithelial cells at corresponding stages of active
proliferation or differentiation. We present here a structural comparison
between these cell line HS species to establish the nature of the changes
that occur in the biosynthesis of HS. A combination of chemical and
enzymatic cleavage, low pressure chromatography and strong anion-exchange
HPLC were used to generate full chain models of each species. Overall, the
HS pools synthesized in the dividing cell line pools possessed less complex
sulfation than those derived from more differentiated, growth arrested
cells.
相似文献
65.
MOTIVATION: Recently, we described a Maximum Weighted Matching (MWM) method
for RNA structure prediction. The MWM method is capable of detecting
pseudoknots and other tertiary base-pairing interactions in a
computationally efficient manner (Cary and Stormo, Proceedings of the Third
International Conference on Intelligent Systems for Molecular Biology, pp.
75-80, 1995). Here we report on the results of our efforts to improve the
MWM method's predictive accuracy, and show how the method can be extended
to detect base interactions formerly inaccessible to automated RNA modeling
techniques. RESULTS: Improved performance in MWM structure prediction was
achieved in two ways. First, new ways of calculating base pair likelihoods
have been developed. These allow experimental data and combined statistical
and thermodynamic information to be used by the program. Second, accuracy
was improved by developing techniques for filtering out spurious base pairs
predicted by the MWM program. We also demonstrate here a means by which the
MWM folding method may be used to detect the presence of base triples in
RNAs. AVAILABILITY: http://www.cshl.org/mzhanglab/tabaska/j axpage. html
CONTACT: tabaska@cshl.org
相似文献
66.
67.
Rossi MS; Barrio E; Latorre A; Quezada-Diaz JE; Hasson E; Moya A; Fontdevila A 《Molecular biology and evolution》1996,13(2):314-323
Both original and colonizer populations of Drosophila buzzatii have been
analyzed for mtDNA restriction polymorphisms. Most of the mtDNA nucleotide
variation in original populations of NW Argentina can be explained by
intrapopulation diversity and only a small fraction can be accounted for by
between-population diversity. Similar results are obtained using either the
estimated number of nucleotide substitutions per site or considering each
restriction site as a locus. Colonizer populations of the Iberian Peninsula
are monomorphic and show only the most common haplotype from the original
populations. Under the infinite island model and assuming that populations
are in equilibrium, fixation indices indicate enough gene flow to explain
why the populations are not structured. Yet, the possibility exists that
populations have not reached an equilibrium after a founder event at the
end of the last Pleistocene glaciation. Tajima's test suggests that
directional selection and/or a recent bottleneck could explain the present
mtDNA differentiation. Considering the significant population structure
found for the chromosomal and some allozyme polymorphisms, the among-
population uniformity for mtDNA variability argues in favor of the
chromosomal and some allozyme polymorphisms being adaptive.
相似文献
68.
Immunological similarities between specific chloroplast ribosomal proteins from Chlamydomonas reinhardtii and ribosomal proteins from Escherichia coli 总被引:11,自引:0,他引:11
Polyclonal antibodies were elicited against seven of the 33 different
proteins of the large subunit of the chloroplast ribosome from
Chlamydomonas reinhardtii. Three of these proteins are synthesized in the
chloroplast and four are made in the cytoplasm and imported. In western
blots, six of the seven antisera are monospecific for their respective
large subunit ribosomal proteins, and none of these antisera cross-reacted
with any chloroplast small subunit proteins from C. reinhardtii. Antisera
to the three chloroplast-synthesized ribosomal proteins cross-reacted with
specific Escherichia coli large subunit proteins of comparable charge and
molecular weight. Only one of the four antisera to the chloroplast
ribosomal proteins synthesized in the cytoplasm cross-reacted with an E.
coli large subunit protein. None of the antisera cross-reacted with any E.
coli small subunit proteins. On the assumption of a procaryotic,
endosymbiotic origin for the chloroplast, those chloroplast ribosomal
proteins still synthesized within the organelle appear to have retained
more antigenic sites in common with E. coli ribosomal proteins than have
those which are now the products of cytoplasmic protein synthesis. Antisera
to this cytoplasmically synthesized group of chloroplast ribosomal proteins
did not recognize any antigenic sites among C. reinhardtii cytoplasmic
ribosomal proteins, suggesting that the genes for the cytoplasmically
synthesized chloroplast ribosomal proteins either are not derived from the
cytoplasmic ribosomal protein genes or have evolved to a point where no
antigenic similarities remain.
相似文献
69.
W H Cooke I V Ames JE A A Crossman J F Cox T A Kuusela K U Tahvanainen L B Moon J Drescher F J Baisch T Mano B D Levine C G Blomqvist D L Eckberg 《Journal of applied physiology》2000,89(3):1039-1045
We studied three Russian cosmonauts to better understand how long-term exposure to microgravity affects autonomic cardiovascular control. We recorded the electrocardiogram, finger photoplethysmographic pressure, and respiratory flow before, during, and after two 9-mo missions to the Russian space station Mir. Measurements were made during four modes of breathing: 1) uncontrolled spontaneous breathing; 2) stepwise breathing at six different frequencies; 3) fixed-frequency breathing; and 4) random-frequency breathing. R wave-to-R wave (R-R) interval standard deviations decreased in all and respiratory frequency R-R interval spectral power decreased in two cosmonauts in space. Two weeks after the cosmonauts returned to Earth, R-R interval spectral power was decreased, and systolic pressure spectral power was increased in all. The transfer function between systolic pressures and R-R intervals was reduced in-flight, was reduced further the day after landing, and had not returned to preflight levels by 14 days after landing. Our results suggest that long-duration spaceflight reduces vagal-cardiac nerve traffic and decreases vagal baroreflex gain and that these changes may persist as long as 2 wk after return to Earth. 相似文献
70.
Dendritic cells (DCs) are central cells of the immune responses. They can be considered as the most influential antigen-presenting cells in the body because of their unique role in initiating immunity against most types of antigens. Recent studies have clearly established that the state of maturation of DC can be crucial for the ability of these antigen-presenting cells to inhibit or induce T-cell-mediated autoimmune diseases. Type I interferon has been shown to be produced at very high amounts by a specific type of DC (pDC). In recent years, the study of multiple autoimmune diseases has pointed to a central role for type I interferon (IFN-I) in disease pathogenesis, in particular through the IFN-molecular signature deciphered in some of these diseases. One hypothesis would be that IFN directly affects multiple actors of the immune reaction such as T cells and B cells and that it can induce the unabated activation of peripheral dendritic cells. On the other hand, type II IFN has been considered as pathogenic in multiple autoimmune diseases leading to the paradigm of TH-1 type autoimmune diseases. The discovery of the TH-17 type of cells and the protective role IFN-gamma can exert on particular phases of these diseases urge one to re-evaluate this assumption. 相似文献