Role of RNA in facilitating Gag/Gag-Pol interaction.

We have examined the influence of RNA upon the interaction of Gag-Pol with Gag during human immunodeficiency virus type 1 (HIV-1) assembly. COS7 cells were transfected with protease-negative HIV-1 proviral DNA, and Gag/Gag-Pol complexes were detected by coimmunoprecipitation with anti-integrase. In COS7 cells, Gag/Gag-Pol is found almost entirely in pelletable, membrane-bound complexes. Exposure of cells to 1% Triton X-100 releases Gag/Gag-Pol from bulk membrane, but the complexes remain pelletable. The role of RNA in facilitating the interaction between Gag and Gag-Pol was examined in these bulk membrane-free, pelletable complexes. The specific presence of viral genomic RNA is not required to maintain the Gag/Gag-Pol interaction, but some type of RNA is, since exposure to RNase destabilized the Gag/Gag-Pol complex. When present only in Gag, the nucleocapsid mutation R7R10K11S, which inhibits Gag binding to RNA, inhibits the formation of both Gag and Gag/Gag-Pol complexes. When present only in Gag-Pol, this mutation has no effect upon complex formation. This result indicates that Gag-Pol may not interact directly with RNA but rather requires RNA-facilitated Gag multimerization for its interaction with Gag.