Résumé
A single retroviral protein, Gag, is sufficient for virus particle
assembly. While Gag is capable of specifically packaging the genomic
RNA into the particle, this RNA species is unnecessary for particle
assembly in vivo. In vitro, nucleic acids
profoundly enhance the efficiency of assembly by recombinant Gag
proteins, apparently by acting as “scaffolding” in the particle.
To address the participation of RNA in retrovirus assembly in
vivo, we analyzed murine leukemia virus particles that lack
genomic RNA because of a deletion in the packaging signal of the viral
RNA. We found that these particles contain cellular mRNA in place of
genomic RNA. This result was particularly evident when Gag was
expressed by using a Semliki Forest virus-derived vector: under these
conditions, the Semliki Forest virus vector-directed mRNA became very
abundant in the cells and was readily identified in the retroviral
virus-like particles. Furthermore, we found that the retroviral cores
were disrupted by treatment with RNase. Taken together, the data
strongly suggest that RNA is a structural element in retrovirus
particles.