用信息论方法研究几类核酸序列的密码子使用与基因表达水平的关系

研究了Ｅｓｃｈｅｒｉｃｈｉａｃｏｌｉ，Ｂａｃｉｌｌｕｓｓｕｂｔｉｌｉｓ和ｓａｃｃｈａｒｏｍｙｃｅｓＹｅａｓｔ三类核酸序列的密码子使用频率与基因表达水平的关系，依照每一基因中最适密码子、非最适密码子和稀有密码子出现的概率，计算其信息熵Ｅ。首先，发现Ｅ与ＣＡＩ值保持了很好的线性关系，且三类序列的线性拟合方程非常接近，因此，用信息熵Ｅ作为描述基因表达水平的物理量是合适的；其次，三类序列的Ｅ─Ｐ（Ｒ）（稀有密码子概率）曲线都接近对数关系，说明稀有密码子在抑制基因表达水平方面，起着很重要的作用；第三，由各种关系曲线的相似性，可以推测，Ｅ．ｃｏｌｉ等原核生物与真核生物Ｙｅａｓｔ在密码子使用与基因表达水平的关系方面，其机理是相似的。

The Relation between Codon Usage and Gene Expression Level Studied for Three Species with Information Entropy Method

he relations between codon usage frequency and gene expression level are studied for threespecies-E. coli, B. subtilis and Yeast. According to the probabilities of optimal codons and rarecodons, the information entropy E for each sequence is calculated. First, is found that there existsa good linear relation between E and CAI (codon adaption index), and the linear equations forthree species are very similar. So, the information entropy E is an appropriate parameter to de-scribe the gene expression level. Secondly, the curves of E-P(R) (P (R): the probability of rarecodons) for three species are all close to a logarithmic curve, which shows that the rare codonsplay an important role in inhibiting the gene expression. Thirdly, from the similarity of the curvesin three species, it can be inferred that the mechanisms with respect to the codon usage and geneexpression are similar to each other for E. coli, B. subtilis (prokaryote) and Yeast (eukaryote).