Identification of the Nuclear Localization Signal Region of Duck Enteritis Virus UL14 and Its Interaction with VP16

OBJECT: Duck enteritis virus (DEV) is a member of the Alphaherpesvirinae viruses. VP16 and pUL14 are both predicted to be tegument proteins of DEV. METHODS: An indirect immunofluorescence assay (IFA) was performed for preliminary analysis of the colocalization of pUL14 and VP16, which detected their subcellular localization in duck embryo fibroblasts (DEFs) during virus replication. The coexpression of pUL14 and VP16 was detected in transfected DEFs. A bimolecular fluorescence complementation (BiFC) assay was used to confirm a direct interaction between pUL14 and VP16. To better characterize the nuclear localization domain of pUL14, we designed a series of deletion mutants and transfected them with VP16. RESULTS: Our IFA findings indicated that pUL14 binds to VP16 in the cytoplasm and that pUL14 leads VP16 import into the nucleus during DEV replication. The BiFC assay revealed the presence of pUL14 and VP16 complexes. Furthermore, 1-98 amino acid (aa) at the N-terminus of pUL14 played a role in the nuclear localization signal (NLS) region and promoted translocation of VP16 into the nucleus to complete the virus life cycle. CONCLUSIONS: Our findings indicated that pUL14 could transport VP16 into the nucleus and that the N-terminal 1-98 aa may contain the NLS domain of pUL14.