FIG. 1.

RSV infectivity is inhibited by several human APOBEC3 proteins. (A) QCl-3 cells (35 mm culture) were transfected with 2 μg of pRSV/luc, 500 ng of pHIT/G, and 500 ng of pK-βarr (a control), pK-A3B, pK-A3F, or pK-A3G, or 250 ng of pK-A3A or pK-A3C plus 250 ng of the empty pK vector as filler. Lower levels of the A3A and A3C expression plasmids were used in an attempt to achieve equivalent levels of intracellular expression of A3A and A3C, compared to the levels of the three double-CDA APOBEC3 proteins. At 48 h posttransfection, supernatant media were harvested, filtered, and used to infect naïve QCl-3 cells (35 mm culture). A further 24 h later, the infected QCl-3 cells were harvested and lysed, and luciferase activities quantified. Average results of four independent experiments with standard deviations are indicated. The level of luciferase activity induced by RSV virion particles derived from the control culture was arbitrarily set at 100%. (B) The virus producer QCl-3 cultures depicted in panel A were lysed at the time of supernatant harvest and subjected to Western blot analysis using a monoclonal antibody specific for the HA epitope tags found at the carboxy-terminal end of all the APOBEC3 proteins, as well as the β-arr control. Results of a representative experiment are shown.