Influence of SR protein on cellular levels of HIV-1 Gag and Env. 293T cells expressing HIV-1 and one SR protein (either ASF, SC35 or 9G8) were immuno-stained, examined and counted using Confocal Laser Scanning Microscopy (see figure 4). Numbers are representative of more than 100 SR positive cells. For all experiments we evaluated the expression of Gag and Env, and SR protein when applicable. The numbers are expressed as the percentage of all SR positive cells given a DNA transfection efficiency of 70–75% (not shown). When HIV-1 pNL4.3 was transfected alone, 100% of the cells were found to co-express Gag and Env (first bar). Upon co-transfection with the ASF coding DNA, a majority of the cells only expressed ASF and about half of them expressed Gag and the SR protein (see ASF bars). Upon co-transfection of pNL4.3 and either the SC35 or 9G8 coding plasmid, a majority of cells expressed Gag and the SR protein (see SC35 and 9G8 bars).