Flow cytometry analysis of lacZ expression in 293GP, HT1080, or 208F cells transfected by (i) Lipofectin-mediated gene transfer with pLZRNL DNA, (ii) infected with gag pol RNA particles from cell line 293GP-LZRNL in the presence of Lipofectin, or (iii) infected with VSV-G pseudotyped retrovirus prepared from the packaging cell line 293GP-LZRNL. Infected and transfected cells selected by growth in G418 were pooled and assayed for lacZ activity by flow cytometry analysis. In each case, 10,000 live cells were analyzed. The ordinate represents cell numbers and the abscissa represents arbitrary fluorescence emission intensity units.