Involvement of the cytoplasmic domain of the hemagglutinin-neuraminidase protein in assembly of the paramyxovirus simian virus 5

Efficient assembly of enveloped viruses at the plasma membranes of virus-in fected cells requires coordination between cytosolic viral components and v iral integral membrane glycoproteins. As viral glycoprotein cytoplasmic dom ains may play a role in this coordination, we have investigated the importa nce of the hemagglutinin-neuraminidase (HN) protein cytoplasmic domain in t he assembly of the nonsegmented negative-strand RNA paramyxovirus simian vi rus 5 (SV5). By using reverse genetics, recombinant viruses which contain H N with truncated cytoplasmic tails were generated. These viruses were shown to be replication impaired, as judged by small plaque size, reduced replic ation rate, and low maximum titers when compared to those features of wild- type (wt) SV5. Release of progeny virus particles from cells infected with HN cytoplasmic-tail-truncated viruses was inefficient compared to that of w t virus, but syncytium formation was enhanced. Furthermore, accumulation of viral proteins at presumptive budding sites on the plasma membranes of inf ected cells was prevented by HN cytoplasmic tail truncations. We interpret these data to indicate that formation of budding complexes, from which effi cient release of SV5 particles can occur, depends on the presence of an HN cytoplasmic tail.