Structural studies on the authentic mumps virus nucleocapsid showing uncoiling by the phosphoprotein

In this paper, we reveal several insights into how mumps virus (MuV) replicates its RNA genome. The MuV genomic RNA is packaged by the nucleocapsid protein (N), forming a helical structure called the nucleocapsid. The nucleocapsid is the template for RNA synthesis. MuV genomes cannot be copied unless the viral polymerase (vRdRp) can read the sequestered RNA. The MuV phosphoprotein (P) appears to play a central role in this process. In this paper, we provide the first evidence, to our knowledge, of P inducing the nucleocapsid to uncoil. MuV P uses two separate domains to promote viral RNA synthesis. One domain attaches to the nucleocapsid while the other domain relaxes the helical structure to allow vRdRp to easily read the viral genome.