The human APOBEC3G-GFP, pig APOBEC3F-GFP and GFP expression constructs were described previously [28, 41] . The pig and human cell lines were maintained as above. One day prior to transfection, 5,000-20,000 cells were seeded onto LabTek chambered coverglasses (Nunc). After 24 hrs incubation, these cells were transfected with 250 ng of the relevant plasmid construct. After 24 hrs of additional incubation, images of the live cells were acquired using a Zeiss Axiovert 200 microscope at 4006 total magnification. Images were analyzed using Image J software (http://rsb.info.nih.gov/ij).