Basak Surajit, Mukhopadhyay Pamela, Gupta Sanjib Kumar, Ghosh Tapash Chandra
Biomedical Informatics Center, National Institute of Cholera and Enteric Diseases, P-33, C.I.T Road, Scheme-XM, Beliaghata, Kolkata-700010, India.
Bioinformation. 2010 Feb 28;4(8):352-6. doi: 10.6026/97320630004352.
One of the central issues of evolutionary genomics is to find out the adaptive strategies of microorganisms to stabilize nucleic acid molecules under high temperature. Thermal adaptation hypothesis gives a link between G+C content and growth temperature if there is a considerable variation of guanine and cytosine content between species. However, there has been a long-standing debate regarding the correlations between genomic GC content and optimal growth temperature (Topt). We urged that adaptation to growth at high temperature requires a coordinated set of evolutionary changes affecting: (i) nucleic acid thermostability and (ii) stability of codon-anticodon interactions. Moreover, in Bacillaceae family we have demonstrated that a higher genomic GC level do not have any role in stabilizing mRNA secondary structure at high growth temperature. Comparative analysis between homologous sequences of thermophilic Thermus thermophilus and mesophilic Deinococcus radiodurans suggests that increased levels of GC contents in the coding sequence corresponding to strand structure of Thermus thermophilus genes have stabilizing effect on the mRNA secondary structure, whereas increased levels of GC contents in coding sequences corresponding to aperiodic structure have destabilizing effect on the mRNA secondary structure. In this perspective, a critical review of thermal adaptation hypothesis is further advocated.
进化基因组学的核心问题之一是找出微生物在高温下稳定核酸分子的适应性策略。如果物种间鸟嘌呤和胞嘧啶含量存在显著差异，热适应假说给出了G+C含量与生长温度之间的联系。然而，关于基因组GC含量与最佳生长温度（Topt）之间的相关性一直存在长期争论。我们认为，适应高温生长需要一系列协调的进化变化，这些变化影响：（i）核酸热稳定性和（ii）密码子-反密码子相互作用的稳定性。此外，在芽孢杆菌科中，我们已经证明较高的基因组GC水平在高生长温度下对稳定mRNA二级结构没有任何作用。嗜热栖热菌和嗜温耐辐射球菌同源序列的比较分析表明，与嗜热栖热菌基因链结构相对应的编码序列中GC含量的增加对mRNA二级结构有稳定作用，而与非周期性结构相对应的编码序列中GC含量的增加对mRNA二级结构有破坏作用。从这个角度来看，进一步提倡对热适应假说进行批判性审视。
