Grogan D W
Department of Biological Sciences, University of Cincinnati, OH 45221-0006, USA.
Mol Microbiol. 1998 Jun;28(6):1043-9. doi: 10.1046/j.1365-2958.1998.00853.x.
Rates of chemical decomposition of DNA at the optimal growth temperatures of hyperthermophiles seem incongruent with the requirements of accurate genome replication. The peculiar physiology, ecology and phylogeny of hyperthermophiles combine to suggest that these prokaryotes have solved a molecular problem (spontaneous loss of native DNA structure) of a magnitude that well-studied microorganisms do not face. The failure of DNA base composition to correlate with optimal growth temperature among hyperthermophiles provides indirect evidence that other mechanisms maintain their chromosomal DNA in the duplex form. Studies in vitro indicate that DNA primary structure is more difficult to maintain at extremely high temperature than is secondary structure, yet hyperthermophiles exhibit only modest levels of spontaneous mutation. Radiation sensitivity studies also indicate that hyperthermophiles repair their DNA efficiently in vivo, and underlying mechanisms are beginning to be examined. Several enzymes of DNA metabolism from hyperthermophilic archaea exhibit unusual biochemical features that may ultimately prove relevant to DNA repair. However, genomic sequencing results suggest that many DNA repair genes of hyperthermophilic archaea may not be recognized because they are not sufficiently related to those of well-studied organisms.
在嗜热菌的最佳生长温度下，DNA的化学分解速率似乎与精确基因组复制的要求不一致。嗜热菌独特的生理学、生态学和系统发育学表明，这些原核生物解决了一个分子问题（天然DNA结构的自发丧失），而这个问题是经过充分研究的微生物所没有面临的。嗜热菌中DNA碱基组成与最佳生长温度之间缺乏相关性，这间接证明了其他机制将它们的染色体DNA维持在双链形式。体外研究表明，在极高温度下，DNA一级结构比二级结构更难维持，但嗜热菌的自发突变水平仅为中等。辐射敏感性研究还表明，嗜热菌在体内能有效修复其DNA，其潜在机制正开始得到研究。来自嗜热古菌的几种DNA代谢酶表现出不同寻常的生化特性，最终可能证明与DNA修复有关。然而，基因组测序结果表明，嗜热古菌的许多DNA修复基因可能无法被识别，因为它们与经过充分研究的生物体的基因没有足够的相关性。
