Podlevsky Joshua D, Li Yang, Chen Julian J-L
School of Molecular Sciences, Arizona State University, Tempe, AZ 85287, USA.
School of Molecular Sciences, Arizona State University, Tempe, AZ 85287, USA
Nucleic Acids Res. 2016 Nov 16;44(20):9891-9901. doi: 10.1093/nar/gkw605. Epub 2016 Jul 4.
Telomerase emerged during evolution as a prominent solution to the eukaryotic linear chromosome end-replication problem. Telomerase minimally comprises the catalytic telomerase reverse transcriptase (TERT) and telomerase RNA (TR) that provides the template for telomeric DNA synthesis. While the TERT protein is well-conserved across taxa, TR is highly divergent amongst distinct groups of species. Herein, we have identified the essential functional domains of TR from the basal eukaryotic species Trypanosoma brucei, revealing the ancestry of TR comprising two distinct structural core domains that can assemble in trans with TERT and reconstitute active telomerase enzyme in vitro The upstream essential domain of T. brucei TR, termed the template core, constitutes three short helices in addition to the 11-nt template. Interestingly, the trypanosome template core domain lacks the ubiquitous pseudoknot found in all known TRs, suggesting later evolution of this critical structural element. The template-distal domain is a short stem-loop, termed equivalent CR4/5 (eCR4/5). While functionally similar to vertebrate and fungal CR4/5, trypanosome eCR4/5 is structurally distinctive, lacking the essential P6.1 stem-loop. Our functional study of trypanosome TR core domains suggests that the functional requirement of two discrete structural domains is a common feature of TRs and emerged early in telomerase evolution.
端粒酶在进化过程中出现，成为解决真核生物线性染色体末端复制问题的一个重要方案。端粒酶至少由催化性端粒酶逆转录酶（TERT）和为端粒DNA合成提供模板的端粒酶RNA（TR）组成。虽然TERT蛋白在不同分类群中高度保守，但TR在不同物种组之间差异很大。在此，我们鉴定了基础真核生物布氏锥虫中TR的必需功能域，揭示了TR的起源，它包含两个不同的结构核心域，这两个结构核心域可与TERT反式组装，并在体外重建有活性的端粒酶。布氏锥虫TR的上游必需结构域，称为模板核心，除了11个核苷酸的模板外，还由三个短螺旋组成。有趣的是，锥虫模板核心结构域缺乏在所有已知TR中都存在的普遍存在的假结，这表明这个关键结构元件是后来进化而来的。模板远端结构域是一个短茎环，称为等效CR4/5（eCR4/5）。虽然在功能上与脊椎动物和真菌的CR4/5相似，但锥虫eCR4/5在结构上有独特之处，缺乏必需的P6.1茎环。我们对锥虫TR核心结构域的功能研究表明，两个离散结构域的功能需求是TR的一个共同特征，并且在端粒酶进化早期就出现了。
