Ubiquitin is important for the budding of many retroviruses and other enveloped viruses, but the precise role of ubiquitin in virus budding remains unclear. Here, we characterized the ubiquitination of the matrix (M) protein of a paramyxovirus, parainfluenza virus 5 (PIV5). The PIV5Mprotein (but not the PIV5 nucleocapsid protein) was found to be targeted for monoubiquitination in transfected mammalian cells. Major sites of ubiquitin attachment identified by mass spectrometry analysis were lysine residues at amino acid positions 79/80, 130, and 247. The cumulative mutation of lysine residues 79, 80, and 130 to arginines led to an altered pattern ofMprotein ubiquitination and impaired viruslike particle (VLP) production. However, the cumulative mutation of lysine residues 79, 80, 130, and 247 to arginines restoredMprotein ubiquitination and VLP production, suggesting that ubiquitin is attached to alternative sites on theMprotein when the primary ones have been removed. Additional lysine residues were targeted for mutagenesis based on the UbiPred algorithm. AnMprotein with seven lysine residues changed to arginines exhibited altered ubiquitination and poor VLP production. A recombinant virus encoding anMprotein with seven lysines mutated was generated, and this virus exhibited a 6-fold-reduced maximum titer, with the defect being attributed mainly to the budding of noninfectious particles. The recombinant virus was assembly deficient, as judged by the redistribution of viralMand hemagglutinin-neuraminidase proteins in infected cells. Similar assembly defects were observed for the wild-type (wt) virus after treatment with a proteasome inhibitor. Collectively, these findings suggest that the monoubiquitination of the PIV5Mprotein is important for proper virus assembly and for the budding of infectious particles.
All Science Journal Classification (ASJC) codes
- Insect Science