Osawa S, Jukes T H
Nagoya University, Department of Biology, Japan.
J Mol Evol. 1989 Apr;28(4):271-8. doi: 10.1007/BF02103422.
The genetic code, once thought to be "frozen," shows variations from the universal code. Variations are found in mitochondria, Mycoplasma, and ciliated protozoa. The variations result from reassignment of codons, especially stop codons. The reassignments take place by disappearance of a codon from coding sequences, followed by its reappearance in a new role. Simultaneously, a changed anticodon must appear. We discuss the role of directional mutation pressure in the events, and we also describe the possibility that such events have taken place during early evolution of the genetic code and can occur during its present evolution.
遗传密码曾被认为是“固定不变的”，但现在发现它与通用密码存在差异。这些差异存在于线粒体、支原体和纤毛原生动物中。差异是由密码子的重新分配导致的，尤其是终止密码子。重新分配是通过编码序列中一个密码子的消失，随后它以新的角色重新出现来实现的。同时，必须出现一个改变的反密码子。我们讨论了定向突变压力在这些事件中的作用，并且还描述了此类事件在遗传密码早期进化过程中发生以及在其当前进化过程中可能发生的可能性。
