Cao W, Lu J, Barany F
Department of Microbiology, Hearst Microbiology Research Center, Cornell University Medical College, New York, NY, USA.
Gene. 1997 Sep 15;197(1-2):205-14. doi: 10.1016/s0378-1119(97)00264-3.
Eight TaqI isoschizomer genes, two from Yellowstone National Park, one from Japan, two from New Zealand, two from Portugal, and one from the Azores (1000 miles west of Portugal), were PCR-amplified and sequenced. Sequence alignment of isoschizomers isolated from close geographical locations shows identical or almost identical protein sequences, while isoschizomers from distant sites demonstrate considerable diversity, ranging from 54 to 75% in amino acid identity. Accordingly, these isoschizomers were arranged into four geographical groups, i.e., USA as represented by Thermus aquaticus YT1, Japan by Thermus thermophilus HB8, New Zealand by Thermus filiformis Tok6A1, Portugal by Thermus sp. SM32. The complete ORFs of two new representative genes, tfiTok6A1I and tsp32IR, were obtained by bubble PCR. Unlike M . TaqI-R.TaqI and M . TthHB8I-R . TthHB8I which exhibit an unusual 13-codon overlap, the methylase and endonuclease genes are each separated by 15 nucleotides in the TfiTok6A1I and Tsp32IR restriction-modification systems. Phylogenetic analysis suggests that initially TfiTok6A1I diverged from a common ancestor, then Tsp32IR branched out, and finally TaqI and TthHB8I diverged from each other during evolution.
对八个TaqI同裂酶基因进行了聚合酶链反应（PCR）扩增和测序，其中两个来自黄石国家公园，一个来自日本，两个来自新西兰，两个来自葡萄牙，一个来自亚速尔群岛（位于葡萄牙以西1000英里处）。从地理位置相近处分离得到的同裂酶的序列比对显示，其蛋白质序列相同或几乎相同，而来自遥远地点的同裂酶则表现出相当大的多样性，氨基酸同一性在54%至75%之间。因此，这些同裂酶被分为四个地理组，即以嗜热水生栖热菌YT1为代表的美国组、嗜热栖热菌HB8代表的日本组、丝状栖热菌Tok6A1代表的新西兰组、嗜热栖热菌SM32代表的葡萄牙组。通过气泡PCR获得了两个新的代表性基因tfiTok6A1I和tsp32IR的完整开放阅读框（ORF）。与表现出异常13个密码子重叠的M.TaqI-R.TaqI和M.TthHB8I-R.TthHB8I不同，在TfiTok6A1I和Tsp32IR限制修饰系统中，甲基化酶基因和内切核酸酶基因各由15个核苷酸隔开。系统发育分析表明，最初TfiTok6A1I从一个共同祖先分化出来，然后Tsp32IR分支出去，最后TaqI和TthHB8I在进化过程中彼此分化。
