Mrázek J, Kypr J
Institute of Biophysics, Academy of Sciences of the Czech Republic, Brno.
J Mol Evol. 1994 Nov;39(5):439-47. doi: 10.1007/BF00173412.
We analyzed occurrences of bases in 20,352 introns, exons of 25,574 protein-coding genes, and among the three codon positions in the protein-coding sequences. The nucleotide sequences originated from the whole spectrum of organisms from bacteria to primates. The analysis revealed the following: (1) In most exons, adenine dominates over thymine. In other words, adenine and thymine are distributed in an asymmetric way between the exon and the complementary strand, and the coding sequence is mostly located in the adenine-rich strand. (2) Thymine dominates over adenine not only in the strand complementary to the exon but also in introns. (3) A general bias is further revealed in the distribution of adenine and thymine among the three codon positions in the exons, where adenine dominates over thymine in the second and mainly the first codon position while the reverse holds in the third codon position. The product (A1/T1)x(A2/T2)x(T3/A3) is smaller than one in only a few analyzed genes.
我们分析了20352个内含子、25574个蛋白质编码基因的外显子以及蛋白质编码序列中三个密码子位置的碱基出现情况。核苷酸序列源自从细菌到灵长类动物的全谱系生物体。分析结果如下：（1）在大多数外显子中，腺嘌呤的含量高于胸腺嘧啶。换句话说，腺嘌呤和胸腺嘧啶在外显子和互补链之间呈不对称分布，且编码序列大多位于富含腺嘌呤的链上。（2）不仅在外显子的互补链中胸腺嘧啶占主导，在内含子中也是如此。（3）在外显子的三个密码子位置上，腺嘌呤和胸腺嘧啶的分布还呈现出一种普遍偏向性，其中在第二个密码子位置以及主要在第一个密码子位置上腺嘌呤占主导，而在第三个密码子位置则相反。在所分析的基因中，只有少数基因的乘积（A1/T1）×（A2/T2）×（T3/A3）小于1。
