Huang Y P, Ito J
Department of Microbiology and Immunology, College of Medicine, The University of Arizona, Tucson, AZ 85724, USA.
Nucleic Acids Res. 1998 Dec 1;26(23):5300-9. doi: 10.1093/nar/26.23.5300.
Bacterial DNA polymerase III (family C DNA polymerase), the principal chromosomal replicative enzyme, is known to occur in at least three distinct forms which have provisionally been classified as class I ( Escherichia coli DNA pol C-type), class II ( Bacillus subtilis DNA pol C-type) and class III (cyanobacteria DNA pol C-type). We have identified two family C DNA polymerase sequences in the hyperthermophilic bacterium Thermotoga maritima. One DNA polymerase consisting of 842 amino acid residues and having a molecular weight of 97 213 belongs to class I. The other one, consisting of 1367 amino acid residues and having a molecular weight of 155 361, is a member of class II. Comparative sequence analyses suggest that the class II DNA polymerase is the principal DNA replicative enzyme of the microbe and that the class I DNA polymerase may be functionally inactive. A phylogenetic analysis using the class II enzyme indicates that T.maritima is closely related to the low G+C Gram-positive bacteria, in particular to Clostridium acetobutylicum, and mycoplasmas. These results are in conflict with 16S rRNA-based phylogenies, which placed T.maritima as one of the deepest branches of the bacterial tree.
细菌DNA聚合酶III（C家族DNA聚合酶）是主要的染色体复制酶，已知它至少以三种不同形式存在，暂被分类为I类（大肠杆菌DNA聚合酶C型）、II类（枯草芽孢杆菌DNA聚合酶C型）和III类（蓝细菌DNA聚合酶C型）。我们在嗜热细菌海栖热袍菌中鉴定出了两个C家族DNA聚合酶序列。一种由842个氨基酸残基组成，分子量为97213的DNA聚合酶属于I类。另一种由1367个氨基酸残基组成，分子量为155361的DNA聚合酶是II类的成员。比较序列分析表明，II类DNA聚合酶是该微生物的主要DNA复制酶，而I类DNA聚合酶在功能上可能无活性。使用II类酶进行的系统发育分析表明，海栖热袍菌与低G+C含量的革兰氏阳性细菌密切相关，特别是与丙酮丁醇梭菌和支原体。这些结果与基于16S rRNA的系统发育树不一致，后者将海栖热袍菌置于细菌树最深的分支之一。
