Respiratory syncytial virus (RSV) genome replication, transcription and translation

After the human respiratory syncytial virus A (hRSV A) enters host cells, an initial round of transcription and translation of virally-encoded mRNAs ensues, which is followed by genome replication.<br><br>The negative sense, single-stranded RNA (-ssRNA) genome of the human respiratory syncytial virus (RSV) A is 15.2 kb long and contains 10 genes that encode 11 proteins. The 10 genes, going from the 3' end to the 5' end of the -ssRNA are: 1C (NS1), 1B (NS2), N, P, M, SH, G, F, M2, and L. Except for the M2 gene, each gene encodes one protein. The two overlapping open reading frames (ORFs) of the M2 gene encode proteins M2-1 and M2-2.<br><br>The N gene encodes the nucleoprotein, which forms decameric and hendecameric (11-fold) rings around which viral genomic RNA is packaged. The L and P genes encode the large polymerase subunit and the phosphoprotein polymerase cofactor subunit, respectively, of the RNA-dependent RNA polymerase complex (RdRP) (reviewed in Battles and McLellan 2019). The L protein contains three conserved enzymatic domains: the RNA-dependent RNA polymerase (RdRp) domain, the polyribonucleotidyl transferase (PRNTase or capping) domain, and the methyltransferase (MTase) domain (reviewed in Sutto-Ortiz et al. 2023). The M2-1 product of the M2 gene is a transcription processivity factor, while the M2-2 product of the M2 gene is a nonstructural protein that regulates the switch between transcription and genome replication. The SH, G, and F genes encode three proteins that are embedded in the viral envelope: small hydrophobic protein, attachment protein, and fusion protein, respectively. The secreted isoform of G protein (sG) mediates immune evasion. The NS1 and NS2 genes encode nonstructural proteins that function together to inhibit apoptosis and interferon response in infected cells. For review, please refer to Battles and McLellan 2019.<br><br>The genomic -ssRNA and the antigenome RNA are encapsidated as they are synthesized, and the association of the nascent RNA with the N protein is likely what causes the replicating polymerase to be processive, with the processivity being further augmented by the M2-1 processivity factor (reviewed in Fearns and Deval 2016). The C-terminal arm of the N protein, known to interact with the P protein subunit of RdRP complex, extends above the plane of N decamers. The interaction between N and P proteins may allow the RdRP complex to distort the helical conformation of the nucleocapsid during RNA synthesis. A long beta-hairpin in the N-terminal region of the N protein may be the site of contact with the catalytic L subunit of the RdRP complex. The proposed model for RNA synthesis in RSV is that the RdRP complex induces a hinge movement of the N-terminal region with respect to the C-terminal region of the N protein that allows the polymerase to thread through the template RNA without the need to disassemble the nucleocapsid (Tawar et al. 2009). The hinge movement would enable 11 bases available for readout at a time (Tawar et al. 2009), consistent with the accumulation of abortive transcripts 9-11 nucleotides in length in P protein phosphorylation mutants that impair transcript elongation (Dupuy et al. 1999).<br><br>The M2-2 protein regulates the shift from positive to negative sense RNA synthesis. While the mechanism has not been fully elucidated, M2-2 was shown to directly bind to the L protein and to inhibit positive sense RNA synthesis (reviewed in Noton and Fearns 2015).<br><br>For review, please refer to Collins et al. 2013.

人类呼吸道合胞病毒A型（hRSV A）侵入宿主细胞后，随即发生病毒编码的mRNA的转录和翻译的初始阶段，随后是基因组复制。人类呼吸道合胞病毒A型（RSV A）的负链单链RNA（-ssRNA）基因组长度为15.2 kb，包含10个基因，这些基因编码11种蛋白质。这10个基因，从-ssRNA的3'端至5'端依次为：1C（NS1）、1B（NS2）、N、P、M、SH、G、F、M2和L。除M2基因外，每个基因编码一种蛋白质。M2基因的两个重叠开放阅读框（ORF）编码M2-1和M2-2蛋白。N基因编码核蛋白，该蛋白在病毒基因组RNA包装过程中形成十聚体和十一聚体（11倍）环。L和P基因分别编码RNA依赖性RNA聚合酶复合物（RdRP）的大聚合酶亚基和磷酸蛋白聚合酶辅助因子亚基。L蛋白含有三个保守的酶学结构域：RNA依赖性RNA聚合酶（RdRp）结构域、多核糖核苷酸转移酶（PRNTase或capping）结构域和甲基转移酶（MTase）结构域。M2基因的M2-1产物是一种转录过程性因子，而M2-2产物是一种非结构蛋白，调节转录与基因组复制的转换。SH、G和F基因分别编码三种嵌入病毒包膜中的蛋白：小疏水性蛋白、附着蛋白和融合蛋白。G蛋白的分泌型异构体（sG）介导免疫逃逸。NS1和NS2基因编码的非结构蛋白共同作用，抑制感染细胞中的细胞凋亡和干扰素反应。欲了解更多信息，请参阅Battles和McLellan（2019）。基因组-ssRNA和抗原基因组RNA在合成过程中被包膜，新生RNA与N蛋白的结合可能引起复制聚合酶的进程性，这种进程性通过M2-1进程性因子进一步增强（参阅Fearns和Deval，2016）。已知N蛋白的C端臂与RdRP复合物的P蛋白亚基相互作用，并延伸至N十聚体的平面之上。N和P蛋白之间的相互作用可能允许RdRP复合物在RNA合成过程中扭曲核衣壳的螺旋构象。N蛋白N端区域的一个长β-发夹结构可能是与RdRP复合物的催化L亚基接触的位点。RSV中RNA合成的假设模型是，RdRP复合物诱导N蛋白N端与C端之间的铰链运动，允许聚合酶在不解散核衣壳的情况下通过模板RNA。铰链运动使得每次可以读取11个碱基（Tawar等，2009），这与P蛋白磷酸化突变体中积累的9-11个碱基长度的终止转录一致，这些突变体会损害转录延伸（Dupuy等，1999）。M2-2蛋白调节从正链到负链RNA合成的转换。尽管其机制尚未完全阐明，但M2-2被证明可以直接结合L蛋白，并抑制正链RNA合成（参阅Noton和Fearns，2015）。欲了解更多信息，请参阅Collins等（2013）。