据外媒8月10日报道，研究人员近日利用一种量化单分子测序技术，探测到人类细胞中一类新型MicroRNA，在基因转录方面代表着一个全新的种类，并证实了长久以来的一种假设，哺乳动物细胞能通过直接复制RNA分子来合成RNA。这一研究由美国匹兹堡大学医学院、瑞士日内瓦大学医学院和两家生物科技公司共同进行，相关论文发表在最新一期《自然》（Nature）杂志上。

这是首次证明人类细胞能像复制DNA一样复制RNA。匹兹堡大学医学院计算与系统生物学教授、论文合着者比诺·约翰博士表示，该发现强调了人类细胞中RNA群体的多样性，这些新型RNA对于开拓治疗新路径，尤其对诊断学的发展有重要意义。

长期以来科学家们认为，人类细胞中的所有RNA都从DNA模版复制，以往的记录显示，这次新观察到的从RNA到RNA的复制机制，只存在于植物和简单的有机物如酵母菌中，与一种名为RNA依赖性RNA聚合酶（简称RdRP）有关，这种酶参与关键性细胞调控程序。

这次研究发现，人类细胞中有数千种能直接复制的MicroRNA，而此前这些RNA却未被重视。在对人类细胞和组织中的这些MicroRNA进行整理归类中，研究人员还发现了一些RNA的新种类，包括抗转录的相关短链RNA，它可能是从信使RNA中分离出来的一种未明确的蛋白质编码基因，其RNA复制机制在人类癌细胞战线上无处不在。

这种未编码RNA分子一直被忽视，只因为以前的测序平台很难提供精确的量化测定。其中一家生物科技公司首席科技官帕德里克·米罗斯博士认为，单分子测序在精确广泛的基因程序分析方面具有重要作用，也给临床应用提供了便利。

原文出处：

Nature doi:10.1038/nature09190

New class of gene-termini-associated human RNAs suggests a novel RNA copying mechanism
Philipp Kapranov1,6, Fatih Ozsolak1,6, Sang Woo Kim2,6, Sylvain Foissac3,6, Doron Lipson1, Chris Hart1, Steve Roels1, Christelle Borel4, Stylianos E. Antonarakis4, A. Paula Monaghan5, Bino John2 & Patrice M. Milos1

Helicos BioSciences Corporation, 1 Kendall Sq. Ste B7301 Cambridge, Massachusetts 02139-1671, USA
Department of Computational and Systems Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15260, USA
Integromics, S.L., Grisolía 2, 28760 Tres Cantos, Madrid, Spain
Department of Genetic Medicine and Development, University of Geneva Medical School, University of Geneva, 1 rue Michel-Servet, 1211 Geneva, Switzerland
Department of Neurobiology, University of Pittsburgh, 3501 Fifth Avenue, Pittsburgh, Pennsylvania 15260, USA
These authors contributed equally to this work.

Small (<200 nucleotide) RNA (sRNA) profiling of human cells using various technologies demonstrates unexpected complexity of sRNAs with hundreds of thousands of sRNA species present1, 2, 3, 4. Genetic and in vitro studies show that these RNAs are not merely degradation products of longer transcripts but could indeed have a function1, 2, 5. Furthermore, profiling of RNAs, including the sRNAs, can reveal not only novel transcripts, but also make clear predictions about the existence and properties of novel biochemical pathways operating in a cell. For example, sRNA profiling in human cells indicated the existence of an unknown capping mechanism operating on cleaved RNA2, a biochemical component of which was later identified6. Here we show that human cells contain a novel type of sRNA that has non-genomically encoded 5′ poly(U) tails. The presence of these RNAs at the termini of genes, specifically at the very 3′ ends of known mRNAs, strongly argues for the presence of a yet uncharacterized endogenous biochemical pathway in cells that can copy RNA. We show that this pathway can operate on multiple genes, with specific enrichment towards transcript-encoding components of the translational machinery. Finally, we show that genes are also flanked by sense, 3′ polyadenylated sRNAs that are likely to be capped.