M. Polianova et al., A treshold level of gag expression is required for particle formation in rat cells transformed by avian retroviruses, FOL BIOL, 45(6), 1999, pp. 233-241
To test the hypothesis that the block of polyprotein precursor processing a
nd particle formation in RSV-transformed mammalian cells is due to a low le
vel of pr76(gag) expression, rat tumor cell lines with different amounts of
precursor molecules were used. The wildtype forms of pr76(gag) have been e
xpressed at a high level by use of SV40-based vector and thirty-two stable
transfected cell clones were isolated. The gag protein expression was detec
ted in the cell lysate by immunoblotting. Untransfected cells released no p
roteins that could be detected by immunoprecipitation with anti-RSV serum.
Membrane-enclosed gag precursor-polyprotein molecules and infectious virus
particles from different stably transfected clones have been found in the m
edium. Both immature and mature virions of type C morphology were directly
detected by transmission electron microscopy, Surprisingly, virus-like part
icles of morphology similar to mature type C retroviruses were found enclos
ed within intracellular membranes in a stably transfected nonproducing clon
e.