Telomerase reverse transcriptase genes identified in Tetrahymena thermophila and Oxytricha trifallax
Telomerase reverse transcriptase genes identified in Tetrahymena thermophila and Oxytricha trifallax
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DOI：
10.1073/pnas.95.15.8479
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发表时间：
1998-07-21
影响因子：
11.1
通讯作者：
Cech, TR
中科院分区：
文献类型：
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作者：
Bryan, TM;Sperger, JM;Cech, TR
端粒酶逆转录酶（TERT）是游仆虫、酵母和哺乳动物染色体末端复制酶的催化亚基。然而，在四膜虫端粒酶的蛋白质组分中，这是第一个被发现的，也是研究最深入的一种，目前尚未见报道。因此，四膜虫似乎有可能使用了一种缺乏TERT蛋白的替代端粒酶。我们现在报告的四膜虫嗜热基因的克隆和测序，其编码的蛋白质具有预期的一个端粒酶，包括大尺寸（133 kDa），碱性（计算PI = 10.0），和逆转录酶序列基序与端粒酶特异性功能的属性。四膜虫TERT基因的mRNA表达在接合后2-5小时显著增加，在端粒重新添加到大核DNA分子之前。我们还报告了克隆和测序的直向同源物从尖毛霉trifallax。Oxytricha macronuclear TERT基因没有内含子，而四膜虫有18个内含子。序列比较揭示了一个新的氨基酸序列基序（CP），保守的纤毛原生动物的TERT，并允许细化以前确定的基序，一个系统发育树的已知的TERT遵循的生物体中，他们被发现，符合古老的起源，而不是最近的转座。在真核生物中，端粒酶的保守性支持端粒酶具有保守的核心（端粒酶加上RNA亚基）的模型，而全酶的其他亚基在物种之间变化更大。
Telomerase reverse transcriptase (TERT) has been identified as the catalytic subunit of the chromosome end-replicating enzyme in Euplotes, yeasts, and mammals. However, it was not reported among the protein components of purified tetrahymena telomerase, the first telomerase identified and the most thoroughly studied. It therefore seemed possible that Tetrahymena used an alternative telomerase that lacked a TERT protein. We now report the cloning and sequencing of a Tetrahymena thermophila gene whose encoded protein has the properties expected for a TERT, including large size (133 kDa), basicity (calculated pi = 10.0), and reverse transcriptase sequence motifs with telomerase-specific features. The expression of mRNA from the Tetrahymena TERT gene increases dramatically at 2-5 h after conjugation, preceding de novo addition of telomeres to macronuclear DNA molecules. We also report the cloning and sequencing of the ortholog from Oxytricha trifallax. The Oxytricha macronuclear TERT gene has no introns, whereas that of Tetrahymena has 18 introns, Sequence comparisons reveal a new amino acid sequence motif (CP), conserved among the ciliated protozoan TERTs, and allow refinement of previously identified motifs, A phylogenetic tree of the known TERTs follows the phylogeny of the organisms in which they are found, consistent with an ancient origin rather than recent transposition. The conservation of TERTs among eukaryotes supports the model that telomerase has a conserved core (TERT plus the RNA subunit), with other subunits of the holoenzyme being more variable among species.