Gladyshev Eugene A, Arkhipova Irina R
Department of Molecular and Cellular Biology, Harvard University, Cambridge, MA 02138, USA.
Proc Natl Acad Sci U S A. 2007 May 29;104(22):9352-7. doi: 10.1073/pnas.0702741104. Epub 2007 May 4.
The evolutionary origin of telomerases, enzymes that maintain the ends of linear chromosomes in most eukaryotes, is a subject of debate. Penelope-like elements (PLEs) are a recently described class of eukaryotic retroelements characterized by a GIY-YIG endonuclease domain and by a reverse transcriptase domain with similarity to telomerases and group II introns. Here we report that a subset of PLEs found in bdelloid rotifers, basidiomycete fungi, stramenopiles, and plants, representing four different eukaryotic kingdoms, lack the endonuclease domain and are located at telomeres. The 5' truncated ends of these elements are telomere-oriented and typically capped by species-specific telomeric repeats. Most of them also carry several shorter stretches of telomeric repeats at or near their 3' ends, which could facilitate utilization of the telomeric G-rich 3' overhangs to prime reverse transcription. Many of these telomere-associated PLEs occupy a basal phylogenetic position close to the point of divergence from the telomerase-PLE common ancestor and may descend from the missing link between early eukaryotic retroelements and present-day telomerases.
端粒酶是在大多数真核生物中维持线性染色体末端的酶，其进化起源一直是一个有争议的话题。类佩内洛普元件（PLEs）是最近描述的一类真核生物反转录元件，其特征在于具有GIY-YIG核酸内切酶结构域以及与端粒酶和II类内含子相似的逆转录酶结构域。在此我们报告，在蛭形轮虫、担子菌纲真菌、不等鞭毛类和植物（代表四个不同的真核生物界）中发现的一部分PLEs缺乏核酸内切酶结构域，并且位于端粒处。这些元件的5'截短末端以端粒为导向，通常由物种特异性的端粒重复序列加帽。它们中的大多数在其3'末端或附近还带有几段较短的端粒重复序列，这可能有助于利用富含G的端粒3'突出端来引发逆转录。许多这些与端粒相关的PLEs占据了一个基础的系统发育位置，接近与端粒酶-PLE共同祖先分歧的点，并且可能起源于早期真核生物反转录元件与当今端粒酶之间缺失的环节。
