Inhibition of HIV-1 production by 2nd generation shRNA. 293T cells were co-transfected with 100 ng pLAI, 0.5 ng of renilla luciferase plasmid and 0, 1 and 5 ng of the shRNA constructs. The CA-p24 level in culture supernatant was measured and renilla luciferase expression was measured to control for the transfection efficiency. Values are shown as percentage of the transfection without shRNA. Averages and standard deviations represent at least three independent transfections that were performed in quadruple.