Duck viral enteritis (DVE), an acute and contagious disease, is highly lethal in all ages of birds from the order Anseriformes (ducks, geese, and swans). This disease is characterized by vascular lesions and tissue hemorrhage, as well as gastrointestinal, lymphatic, and nervous impairments [1–3]. Duck enteritis virus (DEV) is the causative agent for DVE and was first recorded in Holland in 1923 , more outbreaks were reported in the North America , Canada , France  and China  et al.
According to the Eighth International Committee on Taxonomy of Viruses (ICTV), DEV (anatid herpesvirus I) is a member of subfamily Alphaherpesvirinae of the family Herpesviridae but not assigned to any genus . Like other alphaherpesviruses, DEV is a large, enveloped virus with four structural components including linear double strand DNA, an icosahedral capsid, an amorphous tegument and a bilayer lipid envelope. In recent years, a lot of DEV genes have been identified and reported, such as glycoprotein B gene, glycoprotein E gene, thymidylate kinase gene, dUTPase pyrophosphatase gene et al [10–12].
The UL16 genes of alphaherpesviruses encode tegument proteins, which are conserved throughout the herpesvirus family. Previous researches have indicated that the UL16 protein of herpes simplex virus type 1 (HSV-1) is not required for viral replication in cell culture, and its function may be in viral DNA packaging, virion assembly, budding, and egress [13–16]. Firstly, UL16 protein binds to nuclear capsids during nuclear egress. Secondly, UL16 protein attaches to DNA- containing C-capsids in the cytoplasm prior to their arrival at the trans-Golgi network (TGN) for maturation budding. Thirdly, UL16 protein interacts with UL11 which is membrane-bound fastened capsids to the menbrane and drived the budding process . During budding events, the UL16 protein provided abridging function between the capsid and the membrane [18–21]. Interaction of the UL16 tegument protein with the capsid of herpes simplex virus is dynamic, with a binding and release mechanism that is regulated by pH and likely involved scysteines. There are 20 cysteines in UL16 protein, including five cysteines that are conserved within a putative zinc finger . After the capsid budding into the TGN, capsid and tegument proteins also encounter an oxidizing and a low pH environment, which is conducive to trigger conformational changes and disulfide bond formation [23, 24]. Subsequently, the virions release to the extracellular medium where the pH returned to 7.4. In the extracellular medium, the interaction of UL16 with capsid is unstable and UL16 protein releases from the capsid to promote capsid to reenter the next cell .
However, the structure and function of DEV UL16 tegument protein remain unknown. In this study, we report the identification, cloning and molecular characterization analysis of the DEV UL16 gene and its prokaryotic expression. These works may provide some insights for further research about characterizations and functions of DEV UL16.