Department of Chemistry, Portland State University, Portland, OR 97207, USA.
BMC Evol Biol. 2010 Mar 23;10:80. doi: 10.1186/1471-2148-10-80.
During the RNA World, molecular populations were probably very small and highly susceptible to the force of strong random drift. In conjunction with Muller's Ratchet, this would have imposed difficulties for the preservation of the genetic information and the survival of the populations. Mechanisms that allowed these nascent populations to overcome this problem must have been advantageous.
Using continuous in vitro evolution experimentation with an increased mutation rate imposed by MnCl2, it was found that clonal 100-molecule populations of ribozymes clearly exhibit certain characteristics of a quasispecies. This is the first time this has been seen with a catalytic RNA. Extensive genotypic sampling from two replicate lineages was gathered and phylogenetic networks were constructed to elucidate the structure of the evolving RNA populations. A common distribution was found in which a mutant sequence was present at high frequency, surrounded by a cloud of mutant with lower frequencies. This is a typical distribution of quasispecies. Most of the mutants in these clouds were connected by short Hamming distance values, indicating their close relatedness.
The quasispecies nature of mutant RNA clouds facilitates the recovery of genotypes under pressure of being removed from the population by random drift. The empirical populations therefore evolved a genotypic resiliency despite a high mutation rate by adopting the characteristics of quasispecies, implying that primordial RNA pools could have used this strategy to avoid extinction.
在 RNA 世界中，分子群体可能非常小，并且极易受到强大随机漂变的影响。与 Muller 的棘轮结合，这将给遗传信息的保存和群体的生存带来困难。允许这些新生群体克服这个问题的机制一定是有利的。
通过使用 MnCl2 施加的增加突变率的连续体外进化实验，发现核酶的克隆 100 分子群体明显表现出准种的某些特征。这是第一次在催化 RNA 中看到这种情况。从两个复制谱系中收集了广泛的基因型采样，并构建了系统发育网络来阐明不断进化的 RNA 群体的结构。发现了一种常见的分布，其中一种突变序列以高频率存在，周围是具有较低频率的突变体云。这是准种的典型分布。这些云中的大多数突变体通过短汉明距离值连接，表明它们的密切相关。
突变 RNA 云的准种性质有助于在随机漂变的作用下从群体中去除时恢复基因型。因此，尽管突变率很高，但经验种群通过采用准种的特征进化出了基因型的弹性，这意味着原始的 RNA 池可能已经使用这种策略来避免灭绝。
