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551.
552.
The salt dependence of the binding constant (K) and enthalpic (ΔH) and entropic (ΔS) components for magnesium binding to
poly-RNA was determined as a function of the concentration and identity of monovalent counter ions (M+). Both ΔH and ΔS were found to vary linearly with ln [M+]. A theoretical analysis of the experimental data revealed that the temperature dependence of the product of the density
of bound counter ions and the electrostatic interaction parameter, δ(m′ψ)/δT, is non-negligible, although it has previously
been ignored. The sign of δ(m′ψ)/δT was negative for poly(A) and positive for poly(U), indicating that the charge density
of poly(A) decreased with temperature, while that of poly(U) increased. These results are related to the distinct solution
structures of the RNA homopolymers. Considerable support was lent to this calorimetric approach by the excellent agreement
obtained in a test comparison between experimental and calculated parameters. From the intercept of energy term versus ln
[M+] plots, the non-electrostatic contributions, ΔH° and ΔS°, were determined. For each polynucleotide, the similarity in ΔG°
over the series of monovalent ions used in each study suggests a compensatory relationship between ΔH° and ΔS°, each of which
shows significant variation. The non-electrostatic contribution to binding of divalent magnesium is generally entropically
favorable and enthalpically unfavorable for both poly(A) and poly(U).
Received: 2 August 1995 / Accepted: 12 October 1995 相似文献
553.
An efficient method for replacement of nucleotide sequences in the D-loop of T. utilis tRNATyr has been developed. An abnormal tRNATyr lacking in tetranucleotide D16-D-Gm-G19 in its D-loop has been reconstructed by this method and shown to accept tyrosine to about 55% of the aminoacylation level observed for intact tRNATyr. This suggests that the deleted sequence itself is not essential for recognition by TyrRS but a conformational instability of the tRNA possibly caused by the disruption of tertiary interactions between the D-loop and T psi C-loop might have influenced the forward reaction rate leading to the decreased level of aminoacylation. 相似文献
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J Itoh K Kinjoh A Ohyama M Nose M Kyogoku 《The journal of histochemistry and cytochemistry》1992,40(11):1675-1683
We studied the localization of T-cells and HLA-DR antigen-bearing (DR+) cells in rheumatoid synovitis by employing an improved two-color immunofluorescent staining (TCIF) technique. With this technique we have successfully identified DR+ activated T-cells in the inflammatory synovium. T-cells expressed HLA-DR antigen when they were in contact with DR+ antigen-presenting cells (APC). In addition, activated T-cells showed characteristic distribution within the synovium: they were found around high endothelial venules, within lymphoid follicles, and in hyperplastic synovial lining, suggesting their involvement in the development of rheumatoid synovial lesions via interaction with synovial DR+ APC lineage cells. These findings may contribute to better understanding of the role of activated T-cells in the histogenesis of rheumatoid synovitis, a typical chronic inflammatory lesion. 相似文献
559.
Oxidative damage to DNA generates aberrant guanine bases such as 2,6-diamino-4-hydroxy-formamido-pyrimidine (Fapy) and 7,8-dihydro-8-oxoguanine (8-oxoG). Although synthetic oligonucleotides containing a single 8-oxoG have been widely used to study enzymatic processing of this lesion, the synthesis of oligonucleotides containing Fapy as a unique lesion has not been achieved to date. In this study, an oligonucleotide containing a single 2,6-diamino-4-hydroxy-5-(N-methyl)formamido-pyrimidine (me-Fapy, a methylated derivative of Fapy) was prepared by a DNA polymerase reaction and the subsequent alkali treatment. The repair activity of Fpg and hOGG1 proteins were compared using oligonucleotide substrates containing me-Fapy and 8-oxoG. 相似文献