The results showed that besides the SUMO-conjugating enzyme UBC9, an annotated E3 SUMO ligase, PIAS3 (Protein Inhibitor of Activated STAT3), was also screened as a novel UL44 binding partner, and the UL44–PIAS3 interaction was further confirmed by a combination of co-immunoprecipitation, GST/His pull-down, HCMV-infection and fluorescent co-localization assays. Here, PIAS3 is linked to infection.