Versatality of Nucleic Acid Structure and its recognition

(i)寡核苷酸结构的通用性。通过拉曼光谱分析，发现了4种不同的糖链构象，分别为GC特异的Bn型、GG特异的Bh型、AT特异的Bn型和AA特异的B型。此外，限制性内切酶的裂解模式可以从双联体序列的结构刚性来合理解释，即最刚性的结构单元（如CA）几乎不被裂解，而软结构单元（如CT）往往是酶的攻击位点。(2)发夹和鼓环结构。发现环结构通过基层相互作用意外地稳定。当环长n=1-3时，发夹环的稳定性最大，而鼓形环的稳定性随着环长的增加而单调降低。(3) tRNA的通用性及其与氨基酰化酶的相互作用。对编码Ile的tRNA _<minor>^<Ile>进行测序，发现其反密码子首字母为新核苷酸，命名为lysidycytidine。在该tRNA的基因中，反密码子的第一个字母是C，而成熟tRNA中被修饰的胞苷识别为a。通过修饰反密码子碱基对氨基酸的可接受性，获得了tRNA的高级结构与其功能之间有趣的关系。(4) dna -蛋白复合物。在3.5 A的分辨率下解析了HU-DNA的单晶结构，明确了HU-HU的相互作用模式和结合寡聚八聚体在晶体单元中的独特取向。对于cro-DNA复合物，通过NMR和CD测量了结合模式及其强度作为结合DNA碱基序列的函数，结果表明，只有操作者的一致序列才能通过复合物的形成诱导cro-DNA和cro-DNA本身的结构变化。

(i) Versatality of the Structure of OligoDNAs. Four different structures characterized by sugar prosphate conformations were demonstrated by ramann spectroscopy, and they were designated as Bn form specific to GC, Bh form to GG, Bn form to AT and B' form to AA sequences. Furthermore, cleavaga pattern of restriction enzymes were reasonably interpreted in terms of structural rigidity of diad sequences, i.e., the most rigid structural unit such as CA was hardly cleaved,whereas soft structural unit such as CT was often an attacked site by the enzymes.(2) Hairpin and Bulge Loop Structures. Loop structures were found to be unexpectedly stablized by base stacking interactions. The stability of hairpin loop was maximum when loop length n=1-3, while the stability of bulge loop monotoneously decreased as an increasing loop length.(3) Versatality of tRNA and its Interaction with Aminoacylase. tRNA _<minor>^<Ile> which codes Ile was sequenced, and the first letter of its anticodon was found to be new nucleotide, lysidylcytidine named as lysidine. In the gene of this tRNA the first letter of the anticodon was C but the modified cytidine in the mature tRNA recognized A. Interesting relations between higher structure of tRNA and its function were obtained by means of acceptability of amino acids by modification of anticodon bases.(4) DNA-Protein Complexes. Single crystal structure of HU-DNA were solved at 3.5 A resolution,and interacting modes of HU-HU and unique orientation of bound oligo octamers in the crystal unit were clarified. As for cro-DNA complex the binding modes and its strength were measured by NMR and CD as a function of base sequence of base sequence of bound DNA, as the reslts concluded that only the consensus sequence for the operator induced the structural changes in both cro protein and DNA itself by complex formation.