Faculty of Bioengineering and Bioinformatics, Lomonosov Moscow State University, Moscow 199911, Russia.
A. A. Kharkevich Institute for Information Transmission Problems RAS, Moscow 127051, Russia.
Proc Natl Acad Sci U S A. 2023 May 30;120(22):e2221683120. doi: 10.1073/pnas.2221683120. Epub 2023 May 22.
The triplet nature of the genetic code is considered a universal feature of known organisms. However, frequent stop codons at internal mRNA positions in ciliates ultimately specify ribosomal frameshifting by one or two nucleotides depending on the context, thus posing a nontriplet feature of the genetic code of these organisms. Here, we sequenced transcriptomes of eight species and assessed evolutionary patterns arising at frameshift sites. We show that frameshift sites are currently accumulating more rapidly by genetic drift than they are removed by weak selection. The time needed to reach the mutational equilibrium is several times longer than the age of and is expected to occur after a several-fold increase in the frequency of frameshift sites. This suggests that are at an early stage of the spread of frameshifting in expression of their genome. In addition, we find the net fitness burden of frameshift sites to be noncritical for the survival of . Our results suggest that fundamental genome-wide changes such as a violation of the triplet character of genetic code can be introduced and maintained solely by neutral evolution.
遗传密码的三联体性质被认为是已知生物的普遍特征。然而，纤毛虫内部 mRNA 位置的频繁终止密码子最终根据上下文指定核糖体移码一个或两个核苷酸，从而构成这些生物体遗传密码的非三联体特征。在这里，我们对 8 个物种的转录组进行了测序，并评估了移码位点产生的进化模式。我们表明，移码位点目前通过遗传漂变积累的速度比它们被弱选择消除的速度更快。达到突变平衡所需的时间比长好几倍，预计在移码位点的频率增加几倍后才会发生。这表明 处于其基因组表达中移码扩展的早期阶段。此外，我们发现移码位点的净适合度负担对于 的生存是非关键的。我们的结果表明，像遗传密码三联体性质的违反这样的基本全基因组变化可以仅通过中性进化引入和维持。
