Leulliot N, Baumruk V, Abdelkafi M, Turpin P Y, Namane A, Gouyette C, Huynh-Dinh T, Ghomi M
Laboratoire de Physicochimie Biomoléculaire et Cellulaire, UPRESA 7033, Université Pierre et Marie Curie, Case 138, 4 Place Jussieu, 75252 Paris Cedex 05, France.
Nucleic Acids Res. 1999 Mar 1;27(5):1398-404. doi: 10.1093/nar/27.5.1398.
High resolution NMR data on UNCG and GNRA tetraloops (where N is any of the four nucleotides and R is a purine) have shown that they contain ribonucleosides with unusual 2'-endo/anti and 3'-endo/syn conformations, in addition to the 3'-endo/anti ones which are regularly encountered in RNA chains. In the current study, Raman spectroscopy has been used to probe these nucleoside conformations and follow the order (hairpin) to disorder (random chain) structural transitions in aqueous phase in the 5-80 degreesC temperature range. Spectral evolution of GCAA and GAAA tetraloops, as formed in very short hairpins with only three G.C base pairs in their stems (T m >60 degreesC), are reported and compared with those previously published on UUCG and UACG tetraloops, for which the syn orientation of the terminal guanine as well as the 2'-endo/anti conformation of the third rC residue have been confirmed by means of vibrational marker bands. Raman data obtained as a function of temperature show that the first uracil in the UUCG tetraloop is stacked and the two middle residues (rU and rC) are in the 2'-endo/anti conformation, in agreement with the previously published NMR results. As far as the new data concerning the GNRA type tetraloops are concerned, they lead us to conclude that: (i) in both cases (GCAA and GAAA tetraloops) the adenine bases are stacked; (ii) the second rC residue in the GCAA tetraloop has a 3'-endo/anti conformation; (iii) the sugar pucker associated with the third rA residue in both tetraloops possibly undergoes a 3'-endo/2'-endo interconversion as predicted by NMR results; (iv) the stem adopts a regular A-form structure; (v) all other nucleosides of these two GNRA tetraloops possess the usual 3'-endo/anti conformation.
关于UNCG和GNRA四环（其中N为四种核苷酸中的任意一种，R为嘌呤）的高分辨率核磁共振数据表明，除了RNA链中常见的3'-内型/反式构象的核糖核苷外，它们还含有具有不寻常的2'-内型/反式和3'-内型/顺式构象的核糖核苷。在当前的研究中，拉曼光谱已被用于探测这些核苷构象，并追踪在5-80摄氏度温度范围内水相中从有序（发夹）到无序（随机链）的结构转变。报道了在茎中只有三个G.C碱基对的非常短的发夹（T m>60摄氏度）中形成的GCAA和GAAA四环的光谱演变，并与先前发表的关于UUCG和UACG四环的光谱演变进行了比较，对于后者，末端鸟嘌呤的顺式取向以及第三个rC残基的2'-内型/反式构象已通过振动标记带得到证实。作为温度函数获得的拉曼数据表明，UUCG四环中的第一个尿嘧啶是堆积的，两个中间残基（rU和rC）处于2'-内型/反式构象，这与先前发表的核磁共振结果一致。就有关GNRA型四环的新数据而言，它们使我们得出以下结论：（i）在两种情况下（GCAA和GAAA四环），腺嘌呤碱基是堆积的；（ii）GCAA四环中的第二个rC残基具有3'-内型/反式构象；（iii）如核磁共振结果所预测的，两个四环中与第三个rA残基相关的糖环可能经历3'-内型/2'-内型互变；（iv）茎采用规则的A-型结构；（v）这两个GNRA四环的所有其他核苷都具有通常的3'-内型/反式构象。
