Davydov O V
Belarussian Research Institute for Epidemiology and Microbiology, Minsk, Belarus.
J Theor Biol. 1998 Aug 21;193(4):679-90. doi: 10.1006/jtbi.1998.0733.
Up-to-date knowledge is not yet enough to prove or reject completely one of the leading alternative hypotheses considering external or internal origin of the genetic code organization (term "internal" means a peculiarity of amino acids and nucleotides which can propose some logical basis for explanation why definite codons are assigned to particular and not to other amino acids; term "external" in this context implies tRNAs and aminoacyl-tRNA synthetases which provide accuracy of translation but are not presented in the code table in the evident from). New data in favour of the internal approach have been proposed. A close correlation exists between chemical nature of single, the most remote from C alpha, end atoms of amino acid side chains and types of bases in appropriate codon doublets. There are two main rules reflecting this correspondence: (1) all O- or N-ended amino acids (i.e. with O, OO, N, NN, ON, OC and NC end patterns) possess the A-containing codon doublets; (2) all solely C-ended (excluding Ala) and S-ended amino acids (i.e. residues with C, CC and S ends) have the U-containing codon doublets. The discovered asymmetry is characterized by the following high reliable differences of A and U distribution among 21 patterns of individual doublets belonging to 18 amino acids (Pro and Gly are discarded): (a) proportion of A plus U bases corresponding to the two rules, 22/26 is much more than proportion of such bases in violating cases, 4/26; (b) A and U are dominant bases over each of other base types in the doublets of O/N- and C/S-ending amino acids, respectively; (c) the numbers of doublets bearing (18) and not bearing (3) dominant A or U bases are also significantly different. The concept of indicative amino acid end atoms (O/N and non-O/non-N) and doublet A/U bases has been proposed and discussed as so far unknown regulative system of submolecular level of heredity which, additionally to possible key role in the process of the genetic code arising, provides now control of its universality, stability and fidelity.
最新的知识还不足以完全证明或否定关于遗传密码组织的外部或内部起源的主要替代假说之一（术语“内部”是指氨基酸和核苷酸的特性，这可以为解释为什么特定密码子被分配给特定氨基酸而不是其他氨基酸提供一些逻辑基础；在此背景下，术语“外部”意味着tRNA和氨酰tRNA合成酶，它们提供翻译的准确性，但在密码子表中没有明显体现）。有人提出了支持内部方法的新数据。氨基酸侧链中单个的、离α-碳原子最远的末端原子的化学性质与相应密码子双联体中的碱基类型之间存在密切相关性。有两条主要规则反映了这种对应关系：（1）所有以O或N结尾的氨基酸（即具有O、OO、N、NN、ON、OC和NC末端模式）都拥有含A的密码子双联体；（2）所有仅以C结尾（不包括丙氨酸）和以S结尾的氨基酸（即具有C、CC和S末端的残基）都拥有含U的密码子双联体。所发现的不对称性具有以下特征，即在属于18种氨基酸（脯氨酸和甘氨酸被排除）的21种单个双联体模式中，A和U分布存在高度可靠的差异：（a）符合两条规则的A加U碱基的比例，22/26远高于违反规则情况下的此类碱基比例，4/26；（b）在以O/N结尾和以C/S结尾的氨基酸的双联体中，A和U分别是比其他碱基类型更占主导的碱基；（c）带有（18个）和不带有（3个）主导A或U碱基的双联体数量也有显著差异。指示性氨基酸末端原子（O/N和非O/非N）和双联体A/U碱基的概念已被提出并讨论，作为迄今为止未知的遗传亚分子水平调节系统，它除了在遗传密码产生过程中可能起关键作用外，现在还对其通用性、稳定性和保真度进行控制。
