Gupta R S, Bustard K, Falah M, Singh D
Department of Biochemistry, McMaster University, Hamilton, Ontario, Canada.
J Bacteriol. 1997 Jan;179(2):345-57. doi: 10.1128/jb.179.2.345-357.1997.
The 70-kDa heat shock protein (hsp70) sequences define one of the most conserved proteins known to date. The hsp70 genes from Deinococcus proteolyticus and Thermomicrobium roseum, which were chosen as representatives of two of the most deeply branching divisions in the 16S rRNA trees, were cloned and sequenced. hsp70 from both these species as well as Thermus aquaticus contained a large insert in the N-terminal quadrant, which has been observed before as a unique characteristic of gram-negative eubacteria and eukaryotes and is not found in any gram-positive bacteria or archaebacteria. Phylogenetic analysis of hsp70 sequences shows that all of the gram-negative eubacterial species examined to date (which includes members from the genera Deinococcus and Thermus, green nonsulfur bacteria, cyanobacteria, chlamydiae, spirochetes, and alpha-, beta-, and gamma-subdivisions of proteobacteria) form a monophyletic group (excluding eukaryotic homologs which are derived from this group via endosybitic means) strongly supported by the bootstrap scores. A closer affinity of the Deinococcus and Thermus species to the cyanobacteria than to the other available gram-negative sequences is also observed in the present work. In the hsp7O trees, D. proteolyticus and T. aquaticus were found to be the most deeply branching species within the gram-negative eubacteria. The hsp70 homologs from gram-positive bacteria branched separately from gram-negative bacteria and exhibited a closer relationship to and shared sequence signatures with the archaebacteria. A polyphyletic branching of archaebacteria within gram-positive bacteria is strongly favored by different phylogenetic methods. These observations differ from the rRNA-based phylogenies where both gram-negative and gram-positive species are indicated to be polyphyletic. While it remains unclear whether parts of the genome may have variant evolutionary histories, these results call into question the general validity of the currently favored three-domain dogma.
70 kDa热休克蛋白（hsp70）序列定义了迄今为止已知的最保守的蛋白质之一。从解蛋白嗜热放线菌和玫瑰嗜热栖热菌中克隆并测序了hsp70基因，这两种菌被选作16S rRNA树中两个最深分支类群的代表。这两个物种以及嗜热水生栖热菌的hsp70在N端象限含有一个大的插入片段，这一现象以前在革兰氏阴性真细菌和真核生物中被观察到，是其独特特征，而在任何革兰氏阳性细菌或古细菌中均未发现。hsp70序列的系统发育分析表明，迄今为止检测的所有革兰氏阴性真细菌物种（包括嗜热放线菌属和栖热菌属成员、绿色非硫细菌、蓝细菌、衣原体、螺旋体以及变形菌门的α-、β-和γ-亚群）形成一个单系类群（不包括通过内共生方式衍生自该类群的真核同源物），自展分数有力支持这一结论。在本研究中还观察到，嗜热放线菌属和栖热菌属物种与蓝细菌的亲缘关系比与其他可用的革兰氏阴性序列更近。在hsp70树中，解蛋白嗜热放线菌和嗜热水生栖热菌被发现是革兰氏阴性真细菌中分支最深的物种。革兰氏阳性细菌的hsp70同源物与革兰氏阴性细菌分支不同，并且与古细菌表现出更密切的关系并共享序列特征。不同的系统发育方法强烈支持古细菌在革兰氏阳性细菌中的多系分支。这些观察结果与基于rRNA的系统发育不同，在基于rRNA的系统发育中，革兰氏阴性和革兰氏阳性物种均显示为多系的。虽然尚不清楚基因组的某些部分是否可能具有不同的进化历史，但这些结果对当前流行的三域教条的普遍有效性提出了质疑。
