APOBEC3A and infection: Here we show that indeed A3A and A3G potently restrict the infection of the murine retroviruses MLV and MMTV when they are the only human proteins expressed in vivo. Indeed, although we previously demonstrated that endogenous mouse A3 restricts M-MLV and MMTV in vivo[32], [33], in the short-term in vivo infection assay used here, both the A3A and A3G transgenes were more effective at inhibiting infection than the mouse protein, even when expressed at much lower levels (Figure 3).