Members of the apolipoprotein B mRNA editing complex polypeptide 1-like (APOBEC) 
family of enzymes exhibit inhibitory activity against a variety of exogenous and 
endogenous retroviruses including retrotransposons, such as long interspersed 
element 1 (LINE-1). Indeed, human APOBEC3A, APOBEC3B, and APOBEC3F inhibit 
retrotransposition of human LINE-1, mouse IAP and MusD retrotransposons. In our 
study, we examined whether the inhibitory effect of APOBEC3 proteins correlates 
with APOBEC3 ability to bind the LINE-1 ORF1 protein. We examined the 
interactions between the LINE-1 ORF1 protein and the most potent LINE-1 
retrotransposon inhibitors, human APOBEC3A and APOBEC3B, by immunofluorescence 
and immunoprecipitation. Although human APOBEC3A shows the highest inhibitory 
potency against LINE-1 retrotransposon, no direct interactions were identified 
either by immunofluorescence or by co-immunoprecipitation. APOBEC3B binds to 
LINE-1 ORF1 protein, yet no co-localization was detected. We concluded that 
APOBEC3 proteins interfere indirectly with the LINE-1 retrotransposition 
pathway, probably through interference with RNA targeting.