High guanine-cytosine content is not an adaptation to high temperature: a comparative analysis amongst prokaryotes
High guanine-cytosine content is not an adaptation to high temperature: a comparative analysis amongst prokaryotes
复制标题
DOI：
10.1098/rspb.2000.1397
复制
发表时间：
2001-03-07
影响因子：
4.7
通讯作者：
Merchant, AR
中科院分区：
文献类型：
--
作者：
Hurst, LD;Merchant, AR
基因组间鸟嘌呤（G）和胞嘧啶（C）含量差异的原因是进化基因组学的核心问题之一。热适应假说推测，由于DNA中的G：C对比腺嘌呤：胸腺嘧啶对更热稳定，因此高GC含量可能是对高温的选择性反应。许多原核生物的基因组GC含量和最佳生长温度的数据汇编未能证明预测的相关性。相比之下，结构RNA的GC含量在高温下更高。我们在这里要解决的问题是，外显子中更自由进化的位点（即密码子第三位置）是否以与整个基因组DNA相同的方式进化，没有显示出相关的反应，或者像结构RNA一样显示出强相关性。后一种模式将为热适应假说提供强有力的支持，因为直链淀粉基因之间GC含量的变化通常在密码子第三位点（GC（3））最深刻地观察到。对完全测序的原核基因组的简单分析表明，嗜热物种的GC（3）平均较高，而不是基因组GC。这表明，如果没有别的，这两种措施的结果不能被假定为是相同的。然而，正确的分析需要系统发育控制。因此，在这里，我们报告的GC组成和最佳生长温度超过100个原核生物的比较分析的结果。比较分析未能显示，无论是在古细菌还是真细菌中，最佳生长温度与整个基因组中的GC含量之间存在任何联系，在蛋白质编码区，或者更重要的是，在GC（3）。相反，可比较的分析证实，结构RNA的GC含量与最佳温度密切相关。与热适应假说的预期相反，在原核生物中，即使在相对自由进化的位点，蛋白质编码基因中的GC含量也不能被认为是对热环境的适应。
The causes of the variation between genomes in their guanine (G) and cytosine (C) content is one of the central issues in evolutionary genomics. The thermal adaptation hypothesis conjectures that, as G:C pairs in DNA are more thermally stable than adenonine:thymine pairs, high GC content may be a selective response to high temperature. A compilation of data on genomic GC content and optimal growth temperature for numerous prokaryotes failed to demonstrate the predicted correlation. By contrast, the GC content of structural RNAs is higher at high temperatures. The issue that we address here is whether more freely evolving sites in exons (i.e. codonic third positions) evolve in the same manner as genomic DNA as a whole, showing no correlated response, or like structural RNAs showing a strong correlation. The latter pattern would provide strong support for the thermal adaptation hypothesis, as the variation in GC content between orthologous genes is typically most profoundly seen at codon third sites (GC(3)). Simple analysis of completely sequenced prokaryotic genomes shows that GC(3), but not genomic GC, is higher on average in thermophilic species. This demonstrates, if nothing else, that the results from the two measures cannot be presumed to be the same. A proper analysis, however, requires phylogenetic control. Here, therefore, we report the results of a comparative analysis of GC composition and optimal growth temperature for over 100 prokaryotes. Comparative analysis fails to show, in either Archea or Eubacteria, any hint of connection between optimal growth temperature and GC content in the genome as a whole, in protein-coding regions or, more crucially, at GC(3). Conversely, comparable analysis confirms that GC content of structural RNA is strongly correlated with optimal temperature. Against the expectations of the thermal adaptation hypothesis, within prokaryotes GC content in protein-coding genes, even at relatively freely evolving sites, cannot be considered an adaptation to the thermal environment.