Respiratory syncytial virus (RSV) RNA synthesis occurs in cytoplasmic inclusion bodies (IBs) in which all the components of the viral RNA polymerase are concentrated. In this work, we show that RSV P protein recruits the essential RSV transcription factor M2-1 to IBs independently of the phosphorylation state of M2-1. We also show that M2-1 dephosphorylation is achieved by a complex formed between P and the cellular phosphatase PP1. We identified the PP1 binding site of P, which is an RVxF-like motif located nearby and upstream of the M2-1 binding region. NMR confirmed both P-M2-1 and P-PP1 interaction regions in P. When the P–PP1 interaction was disrupted, M2-1 remained phosphorylated and viral transcription was impaired, showing that M2-1 dephosphorylation is required, in a cyclic manner, for efficient viral transcription. IBs contain substructures called inclusion bodies associated granules (IBAGs), where M2-1 and neo-synthesized viral mRNAs concentrate. Disruption of the P–PP1 interaction was correlated with M2-1 exclusion from IBAGs, indicating that only dephosphorylated M2-1 is competent for viral mRNA binding and hence for a previously proposed post-transcriptional function.

呼吸道合胞病毒（RSV）RNA合成发生在胞浆内含体（IBs）中，其中病毒RNA聚合酶的所有成分均被浓缩。在这项工作中，我们表明RSV P蛋白独立于M2-1的磷酸化状态将必需的RSV转录因子M2-1募集到IBs。我们还表明，M2-1的去磷酸化是通过P与细胞磷酸酶PP1之间形成的复合物实现的。我们确定了P的PP1结合位点，这是一个位于M2-1结合区附近和上游的RVxF样基序。NMR证实了P中的P-M2-1和P-PP1相互作用区域。当P–PP1相互作用被破坏时，M2-1仍然被磷酸化并且病毒转录受损，这表明需要以循环方式进行M2-1的去磷酸化，用于有效的病毒转录。IBs包含称为包涵体相关颗粒（IBAG）的亚结构，M2-1和新合成的病毒mRNA集中在其中。P–PP1相互作用的中断与IBAG中M2-1的排除有关，表明只有去磷酸化的M2-1才具有病毒mRNA结合的能力，因此具有先前提出的转录后功能。