Versatality of Nucleic Acid Structure and its recognition

(I)寡核苷酸结构的顺序性。用Ramann波谱分析了4种不同的糖芽构象结构，分别命名为GC所特有的Bn形式、GG所特有的Bh形式、AT所特有的Bn形式和AA序列所特有的B‘形式。此外，根据二联体序列的结构刚性合理地解释了限制性内切酶的切割模式，即最刚性的结构单元，如CA几乎不被切割，而软结构单元，如CT，往往是酶攻击的部位。(2)发夹和凸起环结构。发现环状结构意外地被碱基堆积相互作用稳定。当环长n=1~3时，发夹环的稳定性最大，而凸环的稳定性随着环长的增加而单调下降。(3)tRNA的稳定性及其与氨基酰基酶的相互作用。对编码Ile的tRNA_&lt；Minor&gt；^&lt；Ile&gt；进行了序列测定，发现其反密码子的第一个字母为新核苷酸，命名为lysidine。在这个tRNA基因中，反密码子的第一个字母是C，但成熟tRNA中的修饰胞苷识别A。通过对反密码子碱基的修饰，氨基酸的可接受性，获得了tRNA的高级结构与其功能之间的有趣关系。(4)DNA-蛋白质复合体。在3.5A分辨率下解析了HU-DNA的单晶结构，阐明了HU-HU的相互作用模式和结合的寡聚八聚体在晶体单元中的唯一取向。对于cro-DNA复合体，用核磁共振和圆二色谱测量了其结合方式和结合强度随结合DNA碱基序列的变化，结果表明，只有操纵子的共有序列通过形成复合体引起了cro蛋白和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.