Packaging of RdRP complex with replicated hRSV A nucleocapsid

Based on mass spectroscopy of purified viral particles of human respiratory syncytial virus (RSV) A2, the ratio of P protein to M2-1 protein is ~1:1 (Radhakrishnan et al. 2010). This is expected based on the knowledge that this is the ratio in the viral RNA-dependent RNA polymerase (RdRP) complex, where both proteins are present as tetramers. The ratio of the L protein, the catalytic subunit of RdRP, to P protein and M2-1 protein is ~1:3 (Radhakrishnan et al. 2010), close to the expected ratio of 1:4, as the L protein participates as a monomer in the RdRP complex. Slight divergence from the expected ratio may be due to the large size of the L protein (Radhakrishnan et al. 2010). The ratio of P protein and M2-1 protein to N protein is lower than but close to ~1:2 (Radhakrishnan et al. 2010).<br><br>Based on the curatorial estimation that viral genomic RNA is packaged around 209 oligomeric rings of N protein, of which 129 are N decamers (10 N subunits) and 80 are N hendecamers (11 N subunits), and taking into consideration the experimentally determined length of RSV genomic RNA (Bose et al. 2015), number of genomic RNA nucleotides bound by each N subunit (Tawar et al. 2009), and the ratio of N decamers to N hendecamers in RSV nucleocapsids (Tran et al. 2007), the total number of N proteins in a viral nucleocapsid is expected to be 2170. If each N oligomeric ring binds one RdRP complex, this would result in the total number of 832 P proteins, 832 M2-1 proteins, and 209 L proteins in a viral particle. This is close to the ratios observed by mass spectrometry analysis.<br><br>Virion assembly occurs in cytoplasmic inclusion bodies localized in the vicinity of the plasma membrane region where virus filaments, which represent budding virions, form. Each infected cell usually contains several viral inclusion bodies of irregular shape and varying sizes (Radhakrishnan et al. 2010).

基于对人类呼吸道合胞病毒A2型病毒颗粒纯化物的质谱分析，P蛋白与M2-1蛋白的比例约为1:1（Radhakrishnan等，2010年）。此比例符合病毒RNA依赖性RNA聚合酶（RdRP）复合物中的比例，其中两种蛋白均以四聚体的形式存在。L蛋白，即RdRP的催化亚基，与P蛋白和M2-1蛋白的比例约为1:3（Radhakrishnan等，2010年），接近预期的1:4比例，因为L蛋白在RdRP复合物中以单体形式参与。与预期比例的微小偏差可能归因于L蛋白的大尺寸（Radhakrishnan等，2010年）。P蛋白与M2-1蛋白与N蛋白的比例低于预期，但接近于1:2（Radhakrishnan等，2010年）。

根据对病毒基因组RNA围绕209个N蛋白寡聚环的包装估计，其中129个为N十聚体（10个N亚基）和80个为N十一聚体（11个N亚基），并考虑到实验确定的RSV基因组RNA长度（Bose等，2015年）、每个N亚基结合的基因组RNA核苷酸数量（Tawar等，2009年）以及RSV核衣壳中N十聚体与N十一聚体的比例（Tran等，2007年），预计病毒核衣壳中的N蛋白总数为2170个。如果每个N寡聚环结合一个RdRP复合物，这将导致病毒颗粒中P蛋白、M2-1蛋白和L蛋白的总数分别为832个、832个和209个。这一比例与质谱分析观察到的比例相近。

病毒组装发生在细胞质内质膜区域附近的细胞质包涵体中，该区域是病毒丝（代表新形成的病毒颗粒）形成的地方。每个感染细胞通常含有几个形状不规则、大小不一的病毒包涵体（Radhakrishnan等，2010年）。