遗传密码的局部稳定性和演化
Local stability and evolution of the genetic code
摘要：
已知标准遗传密码对翻译错误和点突变具有鲁棒性。我们研究了标准代码的小修改如何影响其鲁棒性。稳健性根据适当的稳定性函数进行评估，其负变化对应于更稳健的代码。在小的修改下获得的更鲁棒的代码的分数似乎出乎意料地高，范围从0.1到0.4取决于稳定性函数和代码修改的选择，但显着低于随机代码中的相应分数（约一半）。从这个意义上说，标准代码应该被认为是明显的非随机根据以前的意见。稳定性函数的负变化的分布揭示了超过一个标准差的非常突然的下降，比高斯分布或在编码氨基酸或终止密码子的集合中具有相同数目的密码子的随机代码更急剧。这种行为对标准代码整体及其二进制NRN-NYN、NWN-NSN和NMN-NKN块都适用。以前，已经证明这种二进制块结构对于代码的鲁棒性是必要的，并且是标准遗传密码所固有的。对应于更鲁棒编码的标准代码的修改可以与代码的不同变体有关。这些效应也可能有助于氨基酸的替代率。观察到的特征表明，在遗传密码的进化过程中，随机因素和自然选择的共同影响。
英文摘要：
The standard genetic code is known to be robust to translation errors and point mutations. We studied how small modifications of the standard code affect its robustness. The robustness was assessed in terms of a proper stability function, the negative variations of which correspond to a more robust code. The fraction of more robust codes obtained under small modifications appeared to be unexpectedly high, ranged from 0.1 to 0.4 depending on the choice of stability function and code modifications, yet significantly lower than the corresponding fraction in the random codes (about a half). In this sense the standard code ought to be considered distinctly non-random in accordance with previous observations. The distribution of the negative variations of stability function revealed very abrupt drop beyond one standard deviation, much sharper than for Gaussian distribution or for the random codes with the same number of codons in the sets coding for amino acids or stop-codons. This behavior holds for both the standard code as a whole and its binary NRN-NYN, NWN-NSN, and NMN-NKN blocks. Previously, it has been proved that such binary block structure is necessary for the robustness of a code and is inherent to the standard genetic code. The modifications of the standard code corresponding to more robust coding may be related to the different variants of the code. These effects may also contribute to the rates of replacements of amino acids. The observed features demonstrate the joint impact of random factors and natural selection during evolution of the genetic code.
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