Localization of the nonstructural protein NS1 in bluetongue virus-infected cells and its presence in virus particles.

Seven monoclonal antibodies to the nonstructural protein NS1 of an Australian isolate of bluetongue virus (BTV) have been used in immunofluoresence and immunogold procedures to locate NS1 in virus-infected cells and cytoskeletons. The antibodies fall into three groups indicating that NS1 contains at least three antigenic sites. One group consists of four antibodies which react solely with cytoskeleton-associated virus-specific tubules. A second group contains one antibody which reacts with cytoskeleton-associated virus particles, released viruses, and purified virus and core particles. Two antibodies constituting a third group react with both tubules and cytoskeleton-associated and released virus particles. NS1 was found in [35S]methionine-labeled, purified virus and core particles. Immunofluorescence tests reveal that those antibodies which react with virus particles also bind to cytoskeleton-associated virus inclusion bodies (VIB). The nature of this association was examined by probing cytoskeletons of BTV-infected cells with antibodies to NS1 and protein A-gold. VIB observed in thin sections were not uniformly labeled. Gold was associated with fibrillar arrays found around virus particles either leaving or in close proximity to the VIB. Fibrillar material was not found in association with all virus particles elsewhere in the cell and this suggests that fibril-virus complexes may be intermediate in virus morphogenesis.