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William Stephenson Papa Nii Asare-Okai Alan A. Chen Scott Tenenbaum Angel E. Garcia Daniele Fabris 《Journal of biomolecular structure & dynamics》2013,31(1)
A stable RNA helix requires at least three base pairs. Surprisingly, a tertiary kissing complex formed between two GACG hairpin loops contains only two GC pairs. In the NMR structure of this complex, the two flanking adenosines stack on the kissing GC pair. This observation raised a possibility that the 5’-dangling adenines contribute to the formation and stability of the kissing interaction. To test this hypothesis, we took a two-pronged approach to examine the effects of various mutational and chemical modifications of the flanking adenosines on the folding of the kissing complex. Using mass spectrometry, we studied formation of kissing dimers formed by different hairpins. Using optical tweezers, we monitored mechanical unfolding of intramolecular kissing complex at single-molecule level. In both experiments, replacing adenine with uridine abolished the kissing interaction, suggesting that a minimal kissing complex must contain two GC pairs flanked by inter-strand stacking adenines. The stabilizing effect by the adenines can be explained by the fact that the stacking purine nucleobases shield the hydrogen bonds of the adjacent GC pairs, preventing them from fraying. Unlike in the context of secondary structure, the 5’-unpaired adenines in the tertiary structure are structurally constrained in a way that allows for effective stacking onto the adjacent base pairs. 相似文献
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Endothelin, a potent peptide agonist in the liver 总被引:8,自引:0,他引:8
Endothelin, a peptide mediator produced by vascular endothelial cells, caused sustained vasoconstriction of the portal vasculature in the perfused rat liver. The vasoactive effect of endothelin was accompanied by increased glycogenolysis and alterations in hepatic oxygen consumption. The endothelin-induced increase in the portal pressure was concentration-dependent with an EC50 of 1 nM. Endothelin-induced hepatic glycogenolysis was dose-dependent but exhibited a different EC50 than for the vasoconstrictive effects of endothelin. Hepatic vasoconstriction and glycogenolysis following endothelin infusion were inhibited when Ca2+ was removed from the perfusion medium. The endothelin-induced responses in the liver were not altered by prior infusion of phenylephrine (alpha-adrenergic agonist), isoproterenol (beta-adrenergic agonist), angiotensin II, glucagon, platelet-activating factor, or the platelet-activating factor antagonist, BN52021. However, repeated infusion of endothelin resulted in desensitization of the glycogenolytic response but was without a significant effect on hepatic vasoconstriction. Endothelin also stimulated metabolism of inositol phospholipids in isolated hepatocytes and Kupffer cells in primary culture. The present experiments demonstrate, for the first time, that endothelin is a very potent agonist in the liver eliciting both a sustained vasoconstriction of the hepatic vasculature and a significant increase in hepatic glucose output. 相似文献
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G. J. Bryan A. J. Collins P. Stephenson A. Orry J. B. Smith M. D. Gale 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1997,94(5):557-563
The development of large panels of simple-to-analyse genetic markers for tagging agronomically important genes and diversity
studies in hexaploid bread wheat is an important goal in applied cereal genetic research. We have isolated and sequenced over
200 clones containing microsatellites from the wheat genome and have tested 153 primer pairs for genetic polymorphism using
a panel of ten wheat varieties, including the parents of our main mapping cross. A subset comprising 49 primer pairs detects
76 loci, of which 74 can be unequivocably allocated to one of the wheat chromosomes. A relatively low frequency of the loci
detected are from the D genome, and these loci show less polymorphism than those from the A and B genomes. Generally, the
microsatellites show high levels of genetic polymorphism and an average of 3.5 alleles per locus with an average polymorphism
information content (PIC), value of 0.51. The observed levels of polymorphism are positively correlated with the length of
the microsatellite repeats. A high proportion, approximately two-thirds, of primer pairs designed to detect simple sequence
repeat (SSR) variation in wheat do not generate the expected amplification products and, more significantly, often generate
unresolvable PCR products. In general, our results agree closely with those obtained from other recent studies using microsatellites
in plants.
Received: 19 March 1996 / Accepted: 28 June 1996 相似文献