PRODUCTION AND CRYSTALLIZATION OF VIRUS-LIKE PARTICLES ASSEMBLED IN AHETEROLOGOUS PROTEIN EXPRESSION SYSTEM

It is of considerable interest to separate the processes of viral infe ctivity and virion assembly. Until recently this has only been possibl e with viruses that could be disassembled and reassembled in vitro. Ev en in these cases it was difficult to establish the authenticity of re assembled capsid protein because of possible irreversible damage that may have occurred to the protein during disassembly. An ideal method f or the study of virus assembly is a protein expression system in which conditions are appropriate for spontaneous particle formation from fr eshly synthesized polypeptides. The baculovirus expression system has proven to be an excellent means to this end. Recently, this approach h as been used to study the T = 3 Flock House insect virus and it has be en demonstrated that subunits with the wild-type protein sequence, and with site-specific mutations that prevent particle maturation, will a ssemble and crystallize. This same approach has now been used at Purdu e to study the T = 4 Nudaurelia omega capensis insect virus. There is no cell culture system currently available for the study of NomegaV, t hus the expression system provides the first opportunity to study asse mbly under controlled conditions.