These observations raised the question whether the altered intranuclear distribution of UL44 observed upon SUMO-1 overexpression affected the viral replication efficiency. To examine the effects of SUMO-1 overexpression on viral DNA replication, U373-Neo and U373-SUMO-1 cells were infected with HCMV at an MOI of 1 and viral DNA levels were measured by quantitative real-time PCR. Viral DNA production from U373-SUMO-1 cells was ,two-fold higher than that from the control cells (U373-Neo and U373-Neo shUbc9; Fig. 6C ). This increase was not observed in Ubc9-knocked down cells (U373-SUMO-1 shUbc9), while the U373-SUMO-1 cells transduced with the non-silencing lentivirus (U373-SUMO-1 NS) exhibited augmented viral DNA levels like the non-transduced U373-SUMO-1 cells (Fig. 6C) .