Bovine leukemia virus Gag particle assembly in insect cells: Formation of chimeric particles by domain-switched leukemia/lentivirus Gag polyprotein

A key stage in the life cycle of C-type retroviruses is the assembly of Gag precursor protein at the plasma membrane of infected cells. Here we report the assembly of bovine leukemia virus (BLV) gag gene product into virus-li ke particles (VLPs) using the baculovirus expression system. Expression of BLV Pr44(Gag) resulted in the assembly and release of VLPs, thereby confirm ing the ability of retroviral Gag polyprotein to assemble and bud from inse ct cells. Efficient particle formation required a myristoylation signal at the N-terminus of BLV Pr44(Gag). Recombinant baculoviruses expressing matri x (MA) or capsid-nucleocapsid (CA-NC) proteins of BLV were generated but ne ither of these domains was capable of assembling into particulate structure s. To assess the compatibility of Gag domains between leukemia and lentivir us groups three different recombinant chimeras each expressing MA of one vi rus (e.g., simian immunodeficiency or BLV) and CA-NC of another (e.g., BLV or human T-cell leukemia virus type-1) were constructed. Each of the chimer ic proteins assembled efficiently and budded as VLPs, suggesting that the M A and CA domains of these two evolutionary divergent retrovirus groups can be functionally exchanged without perturbation of Gag VLP formation. The le nti-leukemia chimeric Gag approach has potential for studying protein-prote in interactions in other retroviruses. (C) 1999 Academic Press.