The role of the respiratory syncytial virus fusion protein in viral filamentous assembly

Abstract

Respiratory syncytial virus (RSV) is a single-stranded RNA virus in the Paramyxoviridae family that is a leading cause of pneumonia and bronchiolitis in infants and the elderly. RSV preferentially assembles and buds from the apical surface of polarized epithelial cells, forming filamentous structures that contain both viral proteins and the genomic RNA. The experiments described in this thesis were designed to identify the host and viral determinants of RSV assembly and budding. First, I show that viral filaments are the likely sites of viral assembly at the cell surface. Interestingly, these data also show that viral filaments are formed by selective sorting of viral proteins into filaments and the exclusion of host cytosolic and membrane proteins. Second, I identify viral determinants of filamentous assembly by showing that a specific phenylalanine amino acid in the fusion protein cytoplasmic tail is necessary for incorporation of internal virion proteins into virus-like filaments. Furthermore, the same phenylalanine residue was shown to be important for incorporation of internal virion proteins into virus-like particles, indicating that the phenylalanine residue is required for both assembly and budding. Finally, I discuss the viral interactions with the host cell as explored by yeast two-hybrid screens. The data show that a number of host proteins localize to viral structures, but none are essential for viral replication. Collectively, these studies suggest that the fusion protein cytoplasmic tail is critical for virus assembly and that viral proteins are the driving factors in RSV assembly and budding.