ERVW-1 and infection: Our work showing that (1) SFN blocks macrophage infection mediated by either VSV-G or HIV-1 Env, (2) SFN does not block infection in all cell-types and (3) blocks replication after late reverse transcription products have been formed, all support a model in which the restriction is well after entry into the cell but likely before the viral pre-integration complex is imported into the cell nucleus.