Oligomerization of Mumps Virus Phosphoprotein

The mumps virus (MuV) genome encodes a phosphoprotein (P) that is important for viral RNA synthesis. P forms the viral RNA-dependent RNA polymerase with the large protein (L). P also interacts with the viral nucleoprotein (NP) and self-associates to form a homotetramer. The P protein consists of three domains, the N-terminal domain (P-N), the oligomerization domain (P-O), and the C-terminal domain (P-C). While P-N is known to relax the NP-bound RNA genome, the roles of P-O and P-C are not clear. In this study, we investigated the roles of P-O and P-C in viral RNA synthesis using mutational analysis and a minigenome system. We found that PN and PC functions can be trans-complemented. However, this complementation requires P-O, indicating that P-O is essential for P function. Using this trans-complementation system, we found that P forms parallel dimers (P-N to P-N and P-C to P-C). Furthermore, we found that residues R231, K238, K253, and K260 in P-O are critical for P's functions. We identified P-C to be the domain that interacts with L. These results provide structure-function insights into the role of MuV P. IMPORTANCE MuV, a paramyxovirus, is an important human pathogen. The P protein of MuV is critical for viral RNA synthesis. In this work, we established a novel minigenome system that allows the domains of P to be complemented in trans. Using this system, we confirmed that MuV P forms parallel dimers. An understanding of viral RNA synthesis will allow the design of better vaccines and the development of antivirals.