RNA-Seq of RNAs encapsidated by Murine Leukemia Virus

Although all retroviruses recruit host cell RNAs into virions, both the spectrum of RNAs encapsidated and the mechanisms by which they are recruited remain largely unknown. Here, we used high-throughput sequencing to obtain a comprehensive description of the RNAs packaged by a model retrovirus, murine leukemia virus. The major encapsidated host RNAs are noncoding RNAs (ncRNAs) and members of the VL30 class of endogenous retroviruses. Remarkably, although MLV assembles in the cytoplasm, precursors to specific tRNAs, small nuclear RNAs (snRNAs) and small nucleolar RNAs are all enriched in virions. Consistent with their cytoplasmic recruitment, packaging of both pre-tRNAs and U6 snRNA requires the nuclear export receptor Exportin-5. Adenylated and uridylated forms of these RNAs accumulate in cells and virions when the cytoplasmic exoribonuclease DIS3L2 and subunits of the RNA exosome are depleted. Together, our data reveal that MLV recruits RNAs from a novel host cell surveillance pathway in which unprocessed and unneeded nuclear ncRNAs are exported to the cytoplasm for degradation.

尽管所有逆转录病毒（retrovirus）均会将宿主细胞RNA招募至病毒粒子（virion）中，但被衣壳化包裹的RNA种类及其招募机制仍尚未完全阐明。本研究利用高通量测序（high-throughput sequencing）技术，对模式逆转录病毒——小鼠白血病病毒（Murine Leukemia Virus, MLV）所包装的RNA进行了全面解析。该病毒衣壳化包裹的主要宿主RNA为非编码RNA（noncoding RNAs, ncRNAs）以及VL30类内源性逆转录病毒（VL30 class of endogenous retroviruses）。值得注意的是，尽管MLV在细胞质（cytoplasm）中进行组装，但特定转运RNA前体（pre-tRNA）、小核RNA（small nuclear RNAs, snRNAs）以及小核仁RNA的前体均在病毒粒子中富集。与其在细胞质中的招募过程相符，转运RNA前体与U6 snRNA的包装均依赖核输出受体（nuclear export receptor）输出蛋白5（Exportin-5）。当细胞质外切核糖核酸酶（cytoplasmic exoribonuclease）DIS3L2与RNA外切体复合物（RNA exosome）的亚基被敲低后，这些RNA的腺苷酸化（adenylated）与尿苷酸化（uridylated）形式会在细胞与病毒粒子中积累。综上，本研究数据表明，MLV从一条全新的宿主细胞监视通路（host cell surveillance pathway）中招募RNA：该通路会将未加工且无用的细胞核非编码RNA转运至细胞质中进行降解。