The herpesvirus VP5 protein encoded by UL19 gene is the major capsid protein. It plays an important role in virus assembly as it comprises the major subunits of the capsomer structure by forming pentons and hexons, containing five and six copies of VP5 molecules, respectively. In both, VP5 molecules are arranged to form an axial channel, which is thought to provide a potential exit route for the internal scaffolding protein. VP5 interacts with other proteins and the morphological intermediates (partial capsids, closed spherical capsids, and polyhedral capsids) are formed in the assembly process. Finally, the mature icosahedral capsid is produced. The recent advances in the characteristics and functions of UL19 gene and its encoding protein VP5 are reviewed to provide a reference for further study of virus assembly and DNA encapsidation.

The codon usage bias of DPV UL19 gene and 25 reference herpesviruses have been analyzed in this study. This work was performed by program CodonW 1.4, and CUSP and CHIPS of EMBOSS. The results indicated that codons of DPV UL19 gene were strong bias towards the synonymous codons with A or T at the third codon position. The codon adaptation index (CAI), effective number of codons (ENC), and GC3s values indicated synonymous codon usage bias in the UL19 gene of herpesviruses, and this synonymous bias was correlated with host evolution. The plot of ENC against GC3s revealed that factors other than gene composition might contribute to the codon usage among the different herpesviruses. The codon usage bias of DPV UL19 gene was compared with that of E. coli, yeast, and Homo sapiens, which might help us understand the relevant mechanism for biased usage of synonymous codons and select appropriate expression systems to improve the expression of target genes. There were 13 codons showing distinct usage differences between DPV and E. coli; 14, between DPV and yeast; and 25, between DPV and Human. We assumed that the DPV UL19 gene might express more efficiently in the E. coli system, yeast as well.