Of note, TZM-bl cells carry the LTR-driven firefly luciferase as well as the β-galactosidase reporter genes to monitor HIV infection; however, we used the GFP reporter in pHR'CMV-GFP vector to quantify infection levels since this vector does not express the Tat protein, which is essential for luciferase and β-galactosidase activation in infected TZM-bl cells; and as GFP expression enables the quantification of large numbers of infected cells through fluorescence-activated cell sorting (FACS) analysis. The gene discussed is TAT; the disease is infection.