NHC Key Laboratory of Systems Biology of Pathogens, Institute of Pathogen Biology, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, People's Republic of China.
College of Biology, Hunan University, Changsha, People's Republic of China.
J Virol. 2019 Nov 13;93(23). doi: 10.1128/JVI.01164-19. Print 2019 Dec 1.
Type A and type B influenza viruses (FluA and FluB viruses) are two major human pathogens that share common structural and functional features. FluA and FluB viruses can reassort within each type but never between the types. Here, we bioinformatically analyzed all promoter sequences of FluA and FluB viruses and confirmed the presence of the type-specific promoter elements. We then studied the promoter elements with cell-based assays and an replication initiation assay. Our results identified, for the first time, a type-specific promoter element-the nucleotide at position 5 in the 3' end of the viral RNA (vRNA)-that plays a key role(s) in modulating polymerase activity in a type-specific manner. Interestingly, swapping the promoter element between FluA and FluB recombinant viruses showed different tolerances: the replacement of FluA virus-specific U5 with FluB virus-specific C5 in influenza virus A/WSN/33 (H1N1) could be reverted to U5 after 2 to 3 passages, while the replacement of FluB virus-specific C5 with FluA virus-specific U5 in influenza virus B/Yamagata/88 could be maintained, but with significantly reduced replication efficiency. Therefore, our findings indicate that the nucleotide variation at position 5 in the 3' end of the vRNA promoter between FluA and FluB viruses contributes to their RNP incompatibility, which may shed new light on the mechanisms of intertypic exclusion of reassortment between FluA and FluB viruses. Genetic reassortment of influenza virus plays a key role in virus evolution and the emergence of pandemic strains. The reassortment occurs extensively within either FluA or FluB viruses but never between them. Here, we bioinformatically compared available promoter sequences of FluA and FluB viruses and confirmed the presence of the type-specific promoter elements. Our and mutagenesis studies showed that a type-specific promoter element-the nucleotide at position 5 in the 3' end of vRNA promoters-plays key roles in modulating polymerase activity. Interestingly, FluA and FluB viruses showed different tolerances upon key promoter element swapping in the context of virus infections. We concluded that the nucleotide at position 5 in the 3' end of the vRNA promoters of FluA and FluB viruses is a critical type-specific determinant. This work has implications for further elucidating the mechanisms of the intertypic exclusion of reassortment between FluA and FluB viruses.
A 型和 B 型流感病毒（FluA 和 FluB 病毒）是两种主要的人类病原体，它们具有共同的结构和功能特征。FluA 和 FluB 病毒可以在同种类型内重配，但永远不会在类型之间重配。在这里，我们通过生物信息学分析了 FluA 和 FluB 病毒的所有启动子序列，并证实了存在类型特异性启动子元件。然后，我们使用基于细胞的测定和复制起始测定研究了启动子元件。我们的结果首次确定了一个类型特异性启动子元件 - 病毒 RNA（vRNA）3'端第 5 位的核苷酸 - 它以类型特异性方式在调节聚合酶活性方面发挥关键作用。有趣的是，在 FluA 和 FluB 重组病毒之间交换启动子元件显示出不同的耐受性：流感病毒 A/WSN/33（H1N1）中用 FluB 病毒特异性 C5 替换 FluA 病毒特异性 U5 可以在 2 到 3 次传代后恢复为 U5，而用 FluB 病毒特异性 C5 替换 FluA 病毒特异性 U5 可以在流感病毒 B/Yamagata/88 中维持，但复制效率显著降低。因此，我们的发现表明 FluA 和 FluB 病毒 vRNA 启动子 3'端第 5 位的核苷酸变异导致它们的 RNP 不兼容，这可能为 FluA 和 FluB 病毒之间重组的类型间排斥的机制提供新的线索。流感病毒的遗传重配在病毒进化和大流行株的出现中起着关键作用。重配在 FluA 或 FluB 病毒内部广泛发生，但从未在它们之间发生。在这里，我们通过生物信息学比较了 FluA 和 FluB 病毒的可用启动子序列，并证实了存在类型特异性启动子元件。我们的和诱变研究表明，一个类型特异性启动子元件 - vRNA 启动子 3'端第 5 位的核苷酸 - 在调节聚合酶活性方面发挥关键作用。有趣的是，在病毒感染的情况下，关键启动子元件交换时，FluA 和 FluB 病毒表现出不同的耐受性。我们得出结论，FluA 和 FluB 病毒 vRNA 3'端第 5 位的核苷酸是一个关键的类型特异性决定因素。这项工作对于进一步阐明 FluA 和 FluB 病毒之间重组的类型间排斥的机制具有重要意义。
