Soto M A, Tohá C J
Biosystems. 1985;18(2):209-15. doi: 10.1016/0303-2647(85)90072-3.
A quantitative rationale for the evolution of the genetic code is developed considering the principle of minimal hardware. This principle defines an optimal code as one that minimizes for a given amount of information encoded, the product of the number of physical devices used by the average complexity of each device. By identifying the number of different amino acids, number of nucleotide positions per codon and number of base types that can occupy each such position with, respectively, the amount of information, number of devices and the complexity, we show that optimal codes occur for 3, 7 and 20 amino acids with codons having a single, two and three base positions per codon, respectively. The advantage of a code of exactly 4 symbols is deduced, as well as a plausible evolutionary pathway from a code of doublets to triplets. The present day code of 20 amino acids encoded by 64 codons is shown to be the most optimal in an absolute sense. Using a tetraplet code further evolution to a code in which there would be 55 amino acids is in principle possible, but such a code would deviate slightly more than the present day code from the minimal hardware configuration. The change from a triplet code to a tetraplet code would occur at about 32 amino acids. Our conclusions are independent of, but consistent with, the observed physico-chemical properties of the amino acids and codon structures. These correlations could have evolved within the constrains imposed by the minimal hardware principle.
基于最小硬件原则，我们推导出了遗传密码进化的定量理论依据。该原则将最优密码定义为，对于给定的编码信息量，使所使用物理设备数量与每个设备平均复杂度的乘积最小的密码。通过分别将不同氨基酸的数量、每个密码子的核苷酸位置数量以及占据每个此类位置的碱基类型数量，与信息量、设备数量和复杂度相对应，我们发现，当氨基酸数量分别为3、7和20，且每个密码子的碱基位置数量分别为1、2和3时，会出现最优密码。我们还推导了恰好由4种符号组成的密码的优势，以及从双联体密码到三联体密码可能的进化途径。结果表明，由64个密码子编码20种氨基酸的现代密码在绝对意义上是最优化的。原则上，使用四联体密码进一步进化为包含55种氨基酸的密码是可能的，但这样的密码与最小硬件配置的偏差会比现代密码略大。从三联体密码到四联体密码的转变将在大约32种氨基酸时发生。我们的结论独立于氨基酸和密码子结构的观察到的物理化学性质，但与之相符。这些相关性可能是在最小硬件原则所施加的限制内进化而来的。
