Cassandra retrotransposons carry independently transcribed 5S RNA
Cassandra retrotransposons carry independently transcribed 5S RNA
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DOI：
10.1073/pnas.0709698105
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发表时间：
2008-04-15
影响因子：
11.1
通讯作者：
Schulman, Alan H.
中科院分区：
文献类型：
--
作者：
Kalendar, Ruslan;Tanskanen, Jaakko;Schulman, Alan H.
我们报告了一组TRIMs（终端重复反转录转座子在微型），这是小的非自主反转录转座子。这些被命名为Cassandra的元件普遍携带保守的5S RNA序列和相关的RNA聚合酶（pol）III启动子和终止子，它们的长末端重复序列（LTR）。它们在所有调查的维管植物中均有发现。对于LTR反转录转座子来说，Cassandra从SS pol III启动子产生无帽的聚腺苷酸化转录物。包含Cassandra序列的加帽通读转录本也可以在RNA和EST数据库中检测到。预测的Cassandra RNA 5S二级结构类似于细胞5S rRNA的二级结构，特别是在pol III启动子区域具有高信息含量。Cassandra的基因整合位点很常见，这是大量反转录转座子的一个不寻常的特征。每个LTR中的5S产生串联5S布置，其5S间间距类似于蜂窝5S的间距。5S基因的分布在开花植物中是非常可变的，并且可以部分地由Cassandra活性解释。因此，卡桑德拉似乎既适应了一种普遍存在的细胞基因，使其成为核糖体RNA的启动子，又寄生了一组尚未确定的逆转录转座子，以获得其生命周期所需的蛋白质。
We report a group of TRIMs (terminal-repeat retrotransposons in miniature), which are small nonautonomous retrotransposons. These elements, named Cassandra, universally carry conserved 5S RNA sequences and associated RNA polymerase (pol) III promoters and terminators in their long terminal repeats (LTRs). They were found in all vascular plants investigated. Uniquely for LTR retrotransposons, Cassandra produces noncapped, polyadenylated transcripts from the SS pol III promoter. Capped, read-through transcripts containing Cassandra sequences can also be detected in RNA and in EST databases. The predicted Cassandra RNA 5S secondary structures resemble those for cellular 5S rRNA, with high information content specifically in the pol III promoter region. Genic integration sites are common for Cassandra, an unusual feature for abundant retrotransposons. The 5S in each LTR produces a tandem 5S arrangement with an inter-5S spacing resembling that of cellular 5S. The distribution of 5S genes is very variable in flowering plants and may be partially explained by Cassandra activity. Cassandra thus appears both to have adapted a ubiquitous cellular gene for ribosomal RNA for use as a promoter and to parasitize an as-yet-unidentified group of retrotransposons for the proteins needed in its lifecycle.