Ghribi S, Maurel M C, Rougee M, Favre A
Institut J. Monod, Laboratoire de Photobiologie Moléculaire, Paris, France.
Nucleic Acids Res. 1988 Feb 11;16(3):1095-112. doi: 10.1093/nar/16.3.1095.
Binding isotherms (20 degrees C) of ethidium bromide to a number of tRNA species at various ionic strengths indicate that i) the number ni of intercalation sites is high 7 to 11 per molecule, in the low salt form III, but small, 2 to 1, at high Mg2+ or Na+ when form I predominates. ii) modification of tRNA at strategic positions for 3D folding prevents full expression of intercalation restriction iii) maximal restriction is obtained at salt concentrations higher than needed for full conversion to form I. It is inferred that restriction, which is not observed with bihelical RNA (or DNA), requires the native tRNA 3D structure but also some physical coupling between the region of 3D folding and bihelical arms. Ribosomal RNAs, some viral RNAs, mRNA from sheep mammary gland as well as the random copolymers Poly UG, Poly AUG, Poly AUCG all exhibit intercalation restriction. Hence 3D folding of the polyribonucleotide chains appears to be a feature common to single-stranded RNAs when free in solution under physiological conditions.
溴化乙锭在不同离子强度下与多种tRNA种类的结合等温线（20摄氏度）表明：i）在低盐的III型中，每分子的嵌入位点数量ni很高，为7至11个，但在高Mg2+或Na+且I型占主导时，该数量很小，为2至1个。ii）在对三维折叠起关键作用的位置对tRNA进行修饰会阻止嵌入限制的完全表达。iii）在高于完全转化为I型所需的盐浓度下可获得最大限制。据推断，双螺旋RNA（或DNA）未观察到这种限制，它需要天然tRNA的三维结构，还需要三维折叠区域与双螺旋臂之间存在某种物理耦合。核糖体RNA、一些病毒RNA、绵羊乳腺的mRNA以及无规共聚物聚UG、聚AUG、聚AUCG均表现出嵌入限制。因此，在生理条件下自由存在于溶液中的多核糖核苷酸链的三维折叠似乎是单链RNA的一个共同特征。
