Envelope virus assembly and budding

For many enveloped viruses, viral matrix and retroviral Gag proteins are able to bud from the cell surface by themselves in the form of lipid-enveloped, virus-like particles (VLPs), suggesting that these proteins play important roles in viral assembly and budding. The major three-types of L-domain motifs, PPxY, P(T/S)AT, and YP(x)(n)L have been identified within these proteins. Many viruses have been shown to commonly utilize cellular ESCRT pathway via direct interaction between the L-domains and the components of the pathway for efficient viral budding. However, for many enveloped viruses, L-domain motifs have not yet been identified, and the involvement of the ESCRT pathway in virus budding is still unknown. Among such viruses, we have been focusing on Sendai virus (SeV) and shown that (i) SeV M functionally and physically interact with a component of the ESCRT complex, Alix/AIP1, although budding of M-VLPs does not seem to be dependent on the pathway; (ii) one of the accessory proteins of SeV, C, also interact with Alix/AIP1, and recruit it to the plasma membrane for efficient budding of M-VLPs; (iii) the C protein regulate balance of viral genome and antigenome RNA synthesis for optimized production of infectious virus particles. These results demonstrate a unique mechanism for budding of SeV as well as a novel mechanism of regulated synthesis of viral genome RNAs for efficient production of infectious particles.