Barbieri Marcello
Dipartimento di Morfologia ed Embriologia, Via Fossato di Mortara 64a, 44121 Ferrara, Italy.
Biosystems. 2019 Nov;185:104024. doi: 10.1016/j.biosystems.2019.104024. Epub 2019 Sep 6.
The experimental evidence has shown that the genetic code is based on arbitrary, or conventional, rules, in the sense that any codon can be associated to any amino acid, and this means that there is no deterministic link between them. This is in sharp contrast with the traditional paradigm of the stereochemical theory, which claims that the rules of the genetic code were determined by chemistry, and more precisely by stereochemical affinities between codons and amino acids. The discovery that the genetic code is based on arbitrary rules, on the other hand, raised a formidable problem: how can such rules exist in Nature? In order to deal with this problem, it has been pointed out that the rules of an arbitrary code could not come fully formed into existence. The first genetic code, in other words, was necessarily ambiguous, and its evolution took place with a mechanism that systematically reduced its ambiguity and eventually removed it. The concept of ambiguity-reduction has been repeatedly mentioned in the scientific literature, but very few papers have actually addressed the problem of its mechanism. One of these papers was published with the name of ribosome-oriented model in order to underline the key role that the ribosomal proteins had in that process, but later on it became clear that other factors had to be taken into account. This is why the ribosome-oriented model had to be extended and here a more general version is proposed with the name of ambiguity-reduction theory.
实验证据表明，遗传密码基于任意的或约定俗成的规则，从这个意义上说，任何密码子都可以与任何氨基酸相关联，这意味着它们之间不存在确定性的联系。这与立体化学理论的传统范式形成了鲜明对比，后者声称遗传密码的规则是由化学决定的，更确切地说是由密码子与氨基酸之间的立体化学亲和力决定的。另一方面，遗传密码基于任意规则这一发现引发了一个棘手的问题：自然界中怎么会存在这样的规则呢？为了解决这个问题，有人指出，任意密码的规则不可能完全现成地存在。换句话说，最初的遗传密码必然是模糊的，其进化是通过一种机制进行的，该机制系统地减少了其模糊性并最终消除了它。减少模糊性的概念在科学文献中被反复提及，但实际上很少有论文探讨其机制问题。其中一篇论文以核糖体导向模型为名发表，以强调核糖体蛋白在该过程中的关键作用，但后来人们清楚地认识到还必须考虑其他因素。这就是为什么核糖体导向模型必须得到扩展，在此提出一个更通用的版本，称为减少模糊性理论。
