Falah M, Gupta R S
Department of Biochemistry, McMaster University, Hamilton, Ontario, Canada.
Int J Syst Bacteriol. 1997 Jan;47(1):38-45. doi: 10.1099/00207713-47-1-38.
A 5.0-kb region containing the hsp70 (dnaK) gene was cloned from Mycoplasma capricolum and sequenced. In addition to the hsp70 gene, this sequence region also contained the complete sequences for the grpE and orfA genes and partial sequences for the clpB and dnaJ genes. The order of the above gene sequences in the cloned fragment was found to be clpB-orfA-grpE-hsp70-dnaJ, which is similar to the order seen in various other gram-positive groups of bacteria. The Hsp70 homologs from two mycoplasma species, Mycoplasma capricolum and Mycoplasma genitalium, contain a number of sequence signatures, including the absence of a large insert in the N-terminal quadrant, that are characteristics of the homologs from gram-positive bacteria and archaebacteria. A detailed phylogenetic analysis based on Hsp70 sequences was also performed. In neighbor-joining and parsimony trees based on Hsp70 sequences, both mycoplasma species branched with the low-G + C-content gram-positive group of bacteria (e.g., Lactobacillus and Erysipelothrix species) in 87% and 96% of the bootstrap replicates, respectively, indicating their close evolutionary relationship to this group. The phylogenetic trees based on Hsp70 sequences show a polyphyletic branching of archaebacteria with the gram-postive species, which is statistically strongly favored.
从山羊支原体中克隆并测序了一个包含hsp70（dnaK）基因的5.0 kb区域。除hsp70基因外，该序列区域还包含grpE和orfA基因的完整序列以及clpB和dnaJ基因的部分序列。发现克隆片段中上述基因序列的顺序为clpB-orfA-grpE-hsp70-dnaJ，这与其他各种革兰氏阳性菌中的顺序相似。来自两种支原体，即山羊支原体和生殖支原体的Hsp70同源物包含许多序列特征，包括在N端象限中没有大的插入片段，这些是革兰氏阳性菌和古细菌同源物的特征。还基于Hsp70序列进行了详细的系统发育分析。在基于Hsp70序列的邻接法和简约法树中，两种支原体物种分别在87%和96%的自展重复中与低G + C含量的革兰氏阳性菌群（如乳酸杆菌属和丹毒丝菌属物种）分支，表明它们与该菌群有密切的进化关系。基于Hsp70序列的系统发育树显示古细菌与革兰氏阳性物种的多系分支，这在统计学上得到强烈支持。
