Wu Chia-Hsin, Chen Pei-Jer, Yeh Shiou-Hwei
Department of Microbiology, National Taiwan University College of Medicine, No. 1, Jen-Ai Road, Section 1, Taipei 10051, Taiwan.
Department of Microbiology, National Taiwan University College of Medicine, No. 1, Jen-Ai Road, Section 1, Taipei 10051, Taiwan; Graduate Institute of Clinical Medicine, National Taiwan University College of Medicine, No. 1, Jen-Ai Road, Section 1, Taipei 10051, Taiwan; National Taiwan University Research Center for Medical Excellence, No. 2, Syu-Jhou Road, Taipei 10055, Taiwan.
Cell Host Microbe. 2014 Oct 8;16(4):462-72. doi: 10.1016/j.chom.2014.09.009.
Coronaviruses contain a positive-sense single-stranded genomic (g) RNA, which encodes nonstructural proteins. Several subgenomic mRNAs (sgmRNAs) encoding structural proteins are generated by template switching from the body transcription regulatory sequence (TRS) to the leader TRS. The process preferentially generates shorter sgmRNA. Appropriate readthrough of body TRSs is required to produce longer sgmRNAs and full-length gRNA. We find that phosphorylation of the viral nucleocapsid (N) by host glycogen synthase kinase-3 (GSK-3) is required for template switching. GSK-3 inhibition selectively reduces the generation of gRNA and longer sgmRNAs, but not shorter sgmRNAs. N phosphorylation allows recruitment of the RNA helicase DDX1 to the phosphorylated-N-containing complex, which facilitates template readthrough and enables longer sgmRNA synthesis. DDX1 knockdown or loss of helicase activity markedly reduces the levels of longer sgmRNAs. Thus, coronaviruses employ a unique strategy for the transition from discontinuous to continuous transcription to ensure balanced sgmRNAs and full-length gRNA synthesis.
冠状病毒含有一条正义单链基因组（g）RNA，该RNA编码非结构蛋白。通过从主体转录调控序列（TRS）到前导TRS的模板转换，产生了几种编码结构蛋白的亚基因组mRNA（sgmRNA）。该过程优先产生较短的sgmRNA。要产生较长的sgmRNA和全长gRNA，需要主体TRS进行适当的通读。我们发现，宿主糖原合酶激酶-3（GSK-3）对病毒核衣壳（N）的磷酸化是模板转换所必需的。GSK-3抑制选择性地减少gRNA和较长sgmRNA的产生，但不影响较短sgmRNA的产生。N磷酸化允许RNA解旋酶DDX1募集到含磷酸化N的复合物中，这促进了模板通读并使得能够合成更长的sgmRNA。DDX1敲低或解旋酶活性丧失显著降低了较长sgmRNA的水平。因此，冠状病毒采用了一种独特的策略来从不连续转录转变为连续转录，以确保sgmRNA和全长gRNA的平衡合成。
