Institut Jacques Monod, CNRS UMR7592, Université Paris Diderot-Paris 7, Bat. Buffon, 75205 Paris Cedex 13, France.
J Mol Evol. 2010 Feb;70(2):181-9. doi: 10.1007/s00239-009-9319-1. Epub 2010 Jan 13.
Previous studies have reported a positive correlation between the GC content of the double-stranded regions of structural RNAs and the optimal growth temperature (OGT) in prokaryotes. These observations led to the hypothesis that natural selection favors an increase in GC content to ensure the correct folding and the structural stability of the molecule at high temperature. To date these studies have focused mainly on ribosomal and transfer RNAs. Therefore, we addressed the question of the relationship between GC content and OGT in a different and universally conserved structural RNA, the RNA component of the signal recognition particle (SRP). To this end we generated the secondary structures of SRP-RNAs for mesophilic, thermophilic, and hyperthermophilic bacterial and archaeal species. The analysis of the GC content in the stems and loops of the SRP-RNA of these organisms failed to detect a relationship between the GC contents in the stems of this structural RNA and the growth temperature of bacteria. By contrast, we found that in archaea the GC content in the stem regions of SRP-RNA is highest in hyperthermophiles, intermediate in thermophiles, and lower in mesophiles. In these organisms, we demonstrated a clear positive correlation between the GC content of the stem regions of their SRP-RNAs and their OGT. This correlation was confirmed by a phylogenetic nonindependence analysis. Thus we conclude that in archaea the increase in GC content in the stem regions of SRP-RNA is an adaptation response to environmental temperature.
先前的研究已经报道了结构 RNA 的双链区的 GC 含量与原核生物的最适生长温度（OGT）之间存在正相关关系。这些观察结果导致了这样的假设，即自然选择有利于增加 GC 含量，以确保分子在高温下正确折叠和结构稳定。迄今为止，这些研究主要集中在核糖体和转移 RNA 上。因此，我们在另一种普遍保守的结构 RNA，即信号识别颗粒（SRP）的 RNA 成分中，研究了 GC 含量与 OGT 之间的关系。为此，我们为中温、嗜热和超嗜热细菌和古细菌物种生成了 SRP-RNA 的二级结构。对这些生物体的 SRP-RNA 茎和环中的 GC 含量进行分析，未能检测到该结构 RNA 的茎中的 GC 含量与细菌的生长温度之间存在关系。相比之下，我们发现古菌的 SRP-RNA 茎区的 GC 含量在超嗜热菌中最高，在嗜热菌中居中，在中温菌中最低。在这些生物体中，我们证明了它们的 SRP-RNA 茎区的 GC 含量与 OGT 之间存在明显的正相关关系。通过非独立性分析证实了这种相关性。因此，我们得出结论，在古菌中，SRP-RNA 茎区 GC 含量的增加是对环境温度的适应反应。
