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A dc conductivity study of native and denatured samples of sodium salts of calf thymus DNA in the solid state was performed at different temperatures and water content. From the results obtained it appears that the major carrier of conductivity is either electronic or ionic, depending upon the temperature of the sample, the water content, and the fact that the conductivity of native samples is higher than that of the denatured ones. These results have been confirmed by dc conductivity studies of poly U and poly A. 相似文献
105.
Luteinizing hormone (LH) has been purified from 150 dromedary pituitaries and its partial physicochemical, biological and immunological characterization has been achieved. Purification of the hormone was monitored by a porcine LH radioreceptor assay (RRA). In this system, the final camLH preparation exhibited an activity 0.6-fold that of highly purified porcine LH. The acid half-dissociation of camLH at equilibrium was observed at pH 4.2. A homologous camLH RRA was developed using the testicular plasma membrane fraction from prepubertal camels and radioiodinated, highly-purified camLH. Pituitary and chorionic gonadotropins (CG) from several mammalian species were compared to camLH in this system. The equine gonadotropins eLH and eCG were shown to be 6 times less potent in the camel RRA than in the porcine RRA, whereas the LH from other species exhibited similar activities in both systems. This particularity of camel LH receptors offers a new tool for the study of structural features of gonatropin interactions with their receptors. 相似文献
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Multiple comparison or alignmentof protein sequences has become a fundamental tool in many different domains in modern molecular biology, from evolutionary studies to prediction of 2D/3D structure, molecular function and inter-molecular interactions etc. By placing the sequence in the framework of the overall family, multiple alignments can be used to identify conserved features and to highlight differences or specificities. In this paper, we describe a comprehensive evaluation of many of the most popular methods for multiple sequence alignment (MSA), based on a new benchmark test set. The benchmark is designed to represent typical problems encountered when aligning the large protein sequence sets that result from today's high throughput biotechnologies. We show that alignmentmethods have significantly progressed and can now identify most of the shared sequence features that determine the broad molecular function(s) of a protein family, even for divergent sequences. However,we have identified a number of important challenges. First, the locally conserved regions, that reflect functional specificities or that modulate a protein's function in a given cellular context,are less well aligned. Second, motifs in natively disordered regions are often misaligned. Third, the badly predicted or fragmentary protein sequences, which make up a large proportion of today's databases, lead to a significant number of alignment errors. Based on this study, we demonstrate that the existing MSA methods can be exploited in combination to improve alignment accuracy, although novel approaches will still be needed to fully explore the most difficult regions. We then propose knowledge-enabled, dynamic solutions that will hopefully pave the way to enhanced alignment construction and exploitation in future evolutionary systems biology studies. 相似文献
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Molecular evolution of mammalian aquaporin-2: further evidence that elephant shrew and aardvark join the paenungulate clade 总被引:1,自引:1,他引:0
Madsen O; Deen PM; Pesole G; Saccone C; de Jong WW 《Molecular biology and evolution》1997,14(4):363-371
A 328-bp sequence from exon 1 of the gene for aquaporin-2 (AQP2) was
compared in 12 mammalian species, representing as many eutherian orders.
This sequence encodes the N-terminal half of this kidney- specific water
channel protein. Most amino acid replacements, as well as an insertion,
have occurred in extracellular loops connecting the transmembrane helices,
in agreement with a lower functional importance of these loops.
Phylogenetic analyses were performed with parsimony, distance, and
maximum-likelihood methods. The AQP2 data set, alone as well as in
combination with previously published alpha A-crystallin protein sequences,
strongly supports a clade consisting of elephant, hyrax, aardvark, and
elephant shrew, reaching bootstrap values of 99%. This finding fully agrees
with the only other presently available sequence data sets that include
these taxa, those of von Willebrand factor and interphotoreceptor
retinoid-binding protein, and suggests that this extended paenungulate
clade is one of the most conspicuous superordinal groupings in eutherian
phylogeny. Some support was obtained for an artiodactyl/perissodactyl
clade, while the grouping of pholidotes with edentates was contradicted.
相似文献
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Alien fishes are considered a major threat to aquatic biodiversity in South Africa, yet relatively little regional information on their biology and ecology is available for many of these species. Seasonal changes in the diet of the bluegill Lepomis macrochirus in Howieson’s Poort Dam, Grahamstown, were assessed during summer and winter in 2014–2015, using stomach content analysis. In winter, juvenile and adult fish diets were dominated by crustacean zooplankton and insects, respectively. In summer, juvenile fish fed on crustaceans and insects, whereas adults consumed mostly fish eggs, indicating a potential impact by these invasive fish on native fish through oophagy. 相似文献
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