Paramyxoviruses are negative-sense single-stranded RNA viruses that comprise many important human and animal pathogens, including human
parainfluenza viruses. These viruses bud from the plasma membrane of infected cells after the viral
ribonucleoprotein complex (vRNP) is transported from the cytoplasm to the cell membrane via Rab11a-marked recycling endosomes. The
viral proteins that are critical for mediating this important initial step in viral assembly are unknown. Here, we used the model paramyxovirus, murine
parainfluenza virus 1, or Sendai virus (SeV), to investigate the roles of
viral proteins in Rab11a-driven virion assembly. We previously reported that
infection with SeV containing high levels of copy-back defective viral genomes (DVGs) (DVG-high SeV) generates heterogenous populations of cells. Cells enriched in full-length (FL) virus produce viral particles containing standard or defective viral genomes, while cells enriched in DVGs do not, despite high levels of defective viral genome replication. Here, we took advantage of this heterogenous cell phenotype to identify
proteins that mediate interaction of vRNPs with Rab11a. We examined the roles of matrix
protein and
nucleoprotein and determined that their presence is not sufficient to drive interaction of vRNPs with recycling endosomes. Using a combination of mass spectrometry and comparative analyses of
protein abundance and localization in DVG-high and FL-virus-high (FL-high) cells, we identified viral polymerase complex component
protein L and, specifically, its
cofactor C as interactors with Rab11a. We found that accumulation of L and C
proteins within the cell is the defining feature that differentiates cells that proceed to viral egress from cells containing viruses that remain in replication phases.IMPORTANCE Paramyxoviruses are members of a family of viruses that include a number of pathogens imposing significant burdens on human health. In particular, human
parainfluenza viruses are an important cause of
pneumonia and
bronchiolitis in children for which there are no
vaccines or directly acting
antivirals. These cytoplasmic replicating viruses bud from the plasma membrane and co-opt cellular endosomal recycling pathways to traffic viral
ribonucleoprotein complexes from the cytoplasm to the membrane of infected cells. The
viral proteins required for viral engagement with the recycling endosome pathway are still not known. Here, we used the model paramyxovirus Sendai virus, or murine
parainfluenza virus 1, to investigate the role of
viral proteins in this initial step of viral assembly. We found that the viral polymerase components large
protein L and accessory
protein C are necessary for engagement with recycling endosomes. These findings are important in identifying
viral proteins as potential targets for development of
antivirals.