The Protein Encoded by the UL3.5 Gene of the Duck Plague Virus Affects Viral Secondary Envelopment, Release, and Cell-to-Cell Spread

Duck plague (DP), caused by duck plague virus (DPV), is a highly contagious and fatal disease among waterfowl. UL3.5, an unconserved gene belonging to the <i>Herpesviridae</i> family, <i>Alphaherpesvirinae</i> subfamily, and <i>Mardivirus</i> genus, is located downstream of UL3 and exhibits high variability in size and sequence, with an absence in herpes simplex virus (HSV). Currently, there is little understanding of DPV UL3.5. In this study, we determined that DPV pUL3.5 is distributed within the cytoplasm and co-located with multiple organelles. In addition, we investigated the genetic type of DPV UL3.5 and found that it is an early gene encoding an early viral protein. To further explore the function of DPV UL3.5, we constructed DPV-BAC-δUL3.5 and discovered that the deletion of UL3.5 significantly impacts the viral secondary envelopment and release processes. Furthermore, the UL3.5-deleted virus shows defects in cell-to-cell spread. In conclusion, our findings demonstrate, for the first time, that the early viral protein encoded by DPV UL3.5 plays a crucial role in promoting viral replication. This offers fundamental insights for further investigations into the function of DPV UL3.5.