RETROVIRUS-LIKE PARTICLES PRODUCED BY VACCINIA VIRUSES EXPRESSING GAG-PRO-POL REGION GENES OF BOVINE LEUKEMIA-VIRUS

Processing and assembly of bovine leukaemia virus-like particles were studied in African green monkey kidney cells using recombinant vaccini a viruses (rVVs) expressing regions of the bovine leukaemia virus geno me. Unprocessed gag precursor protein (Pr44) was detected in immunoblo t analysis of lysed cells and particles sedimented from culture supern atants after infection with a rVV carrying the gag and truncated prote ase (pro) gene. Processing of Pr44 was observed after infection of cel ls with a rVV carrying the gag and pro gene or a rVV expressing the ga g, pro and polymerase (pol) gene. Reverse transcriptase activity was d etected only in association with particles produced by gag-, pro- and pol-expressing recombinants. Thin section electron microscopic analysi s of infected cells and pelleted particles revealed that Pr44 and proc essed gag proteins assembled at the cell membrane. Pr44 was released i nto the cell culture media as immature virus-like particles, whereas p rocessed gag proteins from rVVs expressing gag and pro or gag, pro and pol formed mature particles.