Viral mRNA Translation

Spliced and unspliced viral mRNA in the cytoplasm are translated by host cell ribosomal translation machinery (reviewed in Kash, 2006). At least ten viral proteins are synthesized: HA, NA, PB1, PB2, PA, NP, NS1, NEP/NS2, M1, and M2. Viral mRNA translation is believed to be enhanced by conserved 5'UTR sequences that interact with the ribosomal machinery and at least one cellular RNA-binding protein, G-rich sequence factor 1 (GRSF-1), has been found to specifically interact with the viral 5' UTRs. (Park, 1995; Park, 1999). The viral NS1 protein and the cellular protein P58(IPK) enhance viral translation indirectly by preventing the activation of the translational inhibitor PKR (Salvatore, 2002; Goodman, 2006). The viral NS1 protein has also been proposed to specifically enhance translation through interaction with host poly(A)-binding protein 1 (PABP1) (Burgui, 2003). Simultaneously, host cell protein synthesis is downregulated in influenza virus infection through still uncharacterized mechanisms (Katze, 1986; Garfinkel, 1992; Kash, 2006). In most human influenza A strains (such as PR8), the PB1 mRNA segment is capable of producing a second protein, PB1-F2, from a short +1 open reading frame initiating downstream of the PB1 ORF initiation codon (Chen, 2001).

细胞质中拼接与未拼接的病毒mRNA由宿主细胞核糖体翻译机制进行翻译（参见Kash，2006年综述）。至少有十种病毒蛋白被合成：HA、NA、PB1、PB2、PA、NP、NS1、NEP/NS2、M1和M2。据信，病毒mRNA的翻译通过保守的5'UTR序列与核糖体机制相互作用而得到增强，并且已发现G富集序列因子1（GRSF-1）这一细胞RNA结合蛋白能够特异性地与病毒5' UTRs相互作用。（Park，1995年；Park，1999年）。病毒NS1蛋白与细胞蛋白P58(IPK)通过间接防止翻译抑制因子PKR的激活来增强病毒翻译（Salvatore，2002年；Goodman，2006年）。此外，病毒NS1蛋白还被提议通过与其宿主多聚(A)-结合蛋白1（PABP1）相互作用而特异性地增强翻译（Burgui，2003年）。同时，在流感病毒感染过程中，宿主细胞蛋白的合成通过尚不明确的机制下调（Katze，1986年；Garfinkel，1992年；Kash，2006年）。在大多数人类流感A型病毒株（如PR8）中，PB1 mRNA片段能够从PB1 ORF起始密码子下游的短+1开放阅读框产生第二种蛋白PB1-F2（Chen，2001年）。