SUMO1 and infection: To determine whether theSUMO-1 enhanced block could also be abrogated, 293T cells transduced with theempty vector control or HA-SUMO-1 were pretreated with increasing amounts ofN-MLV containing a green fluorescent protein (GFP) reporter gene (N-MLV GFP).Four hours later, the cells were superinfected with a fixed amount of N-MLV luc.Those 293T cells expressing the empty vector did not significantly restrictN-MLV luc infection (Figure1C).