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

## TL;DR

This study identifies the UL3.5 gene of duck plague virus as essential for viral replication, specifically in secondary envelopment, release, and cell-to-cell spread.

## Contribution

The study reveals the novel role of the DPV UL3.5 gene in viral replication and identifies it as a potential antiviral target.

## Key findings

- UL3.5 encodes an early cytoplasmic protein essential for secondary envelopment and release of the virus.
- Deletion of UL3.5 impairs cell-to-cell spread and viral replication.
- The gene is classified as an early gene and is highly variable in size and sequence.

## Abstract

Duck plague virus (DPV) severely threatens waterfowl, yet the role of its UL3.5 gene remains unknown. This study aimed to define UL3.5’s function by analyzing its protein localization, gene classification, and impact on viral replication. Results show that UL3.5 encodes an early cytoplasmic protein and is essential for viral secondary envelopment, release, and cell-to-cell spread, as its deletion cripples these processes. We conclude that UL3.5 is a key participant in the life cycle of the duck plague virus. These findings unveil a key viral replication mechanism and identify UL3.5 as a potential target for antiviral strategies, offering foundational information for further investigations into the functional characteristics of DPV UL3.5.

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 Herpesviridae family, Alphaherpesvirinae subfamily, and Mardivirus 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.