Identification and characterization of a new E3 ubiquitin ligase in white spot syndrome virus involved in virus latency

White spot syndrome virus (WSSV) is one major pathogen in shrimp aquaculture. WSSV ORF403 is predicted to encode a protein of 641 amino acids, which contains a C3H2C2 RING structure. In the presence of an E2 conjugating enzyme from shrimp, WSSV403 can ubiquitinate itself in vitro, indicating it can function as a viral E3 ligase. Besides, WSSV403 E3 ligase can be activated by a series of E2 variants. Based on RT-PCR and Real time PCR, we detected transcription of WSSV403 in the commercial specific-pathogen-free (SPF) shrimp, suggesting its role as a latency-associated gene. Identified in yeast two-hybrid screening and verified by pull-down assays, WSSV403 is able to bind to a shrimp protein phosphatase (PPs), which was characterized before as an interaction partner for another latent protein WSSV427. Our studies suggest that WSSV403 is a regulator of latency state of WSSV by virtue of its E3 ligase function.