Expression plasmids encoding murine Apobec3, RNaseL or empty vector were co-transfected with an F-MuLV molecular clone, pLRB302, into 293T cells. Serial 3-fold dilutions of the supernatants were used to infect Mus dunni cells, and after 48 h, cells were fixed and stained with a monoclonal antibody (MAb 720) against the FV envelope protein. Foci were counted and infectious titers were calculated per ml of supernatant. Mean fold-differences relative to vector control are shown. P values were calculated using 2-tailed Student’s t test, with p<0.05 considered statistically significant.