Takagi H, Kaneko K, Yomo T
Department of Pure and Applied Sciences, University of Tokyo, Komaba, Meguro-ku, Tokyo 153, Japan.
Artif Life. 2000 Fall;6(4):283-305. doi: 10.1162/106454600300103647.
Evolution of genetic codes is studied as change in the choice of enzymes that are used to synthesize amino acids from the genetic information of nucleic acids. We propose the following theory: the differentiation of physiological states of a cell allows for a choice of enzymes, and this choice is later fixed genetically through evolution. To demonstrate this theory, a dynamical systems model consisting of the concentrations of metabolites, enzymes, amino acyl tRNA synthetase, and tRNA - amino acid complexes in a cell is introduced and studied numerically. It is shown that the biochemical states of cells are differentiated by cell-cell interactions, and each differentiated type starts to use a different synthetase. Through the mutation of genes, this difference in the genetic code is amplified and stabilized. The relevance of this theory to the evolution of non-universal genetic code in mitochondria is suggested. The present theory is based on our recent theory of isologous symbiotic speciation, which is briefly reviewed. According to the theory, phenotypes of organisms are first differentiated into distinct types through the interaction and developmental dynamics, even though they have identical genotypes; later, with mutation in the genotype, the genotype also differentiates into discrete types, while maintaining the "symbiotic" relationship between the types. Relevance of the theory to natural as well as artificial evolution is discussed.
遗传密码的进化被作为从核酸的遗传信息合成氨基酸时所使用的酶的选择变化来研究。我们提出以下理论：细胞生理状态的分化允许酶的选择，并且这种选择随后通过进化在基因上固定下来。为了证明这一理论，引入了一个由细胞内代谢物、酶、氨酰tRNA合成酶和tRNA - 氨基酸复合物的浓度组成的动力学系统模型，并进行了数值研究。结果表明，细胞的生化状态通过细胞间相互作用而分化，并且每种分化类型开始使用不同的合成酶。通过基因突变，遗传密码中的这种差异被放大并稳定下来。该理论与线粒体中非通用遗传密码进化的相关性被提了出来。本理论基于我们最近的同系共生物种形成理论，在此简要回顾一下。根据该理论，生物体的表型首先通过相互作用和发育动力学分化为不同类型，即使它们具有相同的基因型；随后，随着基因型中的突变，基因型也分化为离散类型，同时保持这些类型之间的“共生”关系。讨论了该理论与自然进化以及人工进化的相关性。
