Lack of correlation of A3G oligomerization and packaging competence. HeLa cells were transfected with 2.5 μg each of plasmids expressing A3G wt (wt), W127A, or Y124A mutants in a combination of two as indicated above the figure. Cell lysates were analyzed either directly by immunoblotting with antibodies to A3G (top panel) or tubulin (bottom panel) or subsequent to immunoprecipitation with a Myc-specific monoclonal antibody (middle panel). Untagged A3G variants (no tag) have a faster mobility in the gel than the Myc-tagged variants. The position of the untagged proteins co-immunoprecipitated by the Myc-tagged variants is indicated on the right (co-IP).