Molecular cloning and characterization of pseudorabies virus EP0 gene.

The pseudorabies virus (PRV) early protein EP0 is a homologue of the herpes simplex virus 1 (HSV-1) immediate-early protein ICP0, which is a multifunctional protein and important for HSV-1 infection. However, the exact function of EP0 is not clear. In this study, using polymerase chain reaction, a 1,104 base-pair sequence of the EP0 gene was amplified from the PRV Becker strain genome and identification of the EP0gene was confirmed by further cloning and sequencing. Bioinformatics analysis indicated that the PRV EP0 gene encoded a putative polypeptide with 367 amino acids. The encoded protein, designated as EP0 contained a conserved RING-finger superfamily domain and was found to be closely related with the herpes virus RING-finger superfamily and was highly conserved among the counterparts encoded by RING-finger genes. Multiple nucleic acid sequence and amino-acid sequence alignments suggested that PRV EP0 showed a relatively higher similarity with EP0-like proteins of genus Varicellovirus than with those of other genera of Alphaherpesvirinae. In addition, phylogenetic analysis showed that PRV EP0 had a close evolutionary relationship with members of genus Varicellovirus, especially bovine herpesvirus 1 (BoHV-1) and BoHV-5. Antigen prediction indicated that several potential B-cell epitopes were located in EP0. Also, subcellular localization analysis demonstrated that EP0 was predominantly localized in the nucleus, suggesting that it might function as a nuclear-targeted protein.