The flavivirus protein NS4B recruits the cis-Golgi protein ACBD3 to modify ER-Golgi trafficking for virion release

Flavivirus infection involves extensive remodeling of the endoplasmic reticulum (ER), which is key to both the replication of the viral RNA genome as well as the assembly and release of new virions. Yet, little is known about how viral proteins and host factors cooperatively facilitate such a vast transformation of the ER, and how this influences the different steps of the viral life cycle. In this study, we screened for host proteins that interact with the tick-borne encephalitis virus (TBEV) protein NS4B and found that the top candidates were coupled to trafficking between ER exit sites (ERES) and the Golgi. We characterized the role of ACBD3, one of the identified proteins, in flavivirus infection and show that it interacts with NS4B to promote infection across multiple flavivirus species. Using ACBD3 knockout cells, we found that the depletion of ACBD3 inhibited TBEV replication by preventing the trafficking of virions from the cell. We found that ACBD3 promotes flavivirus infection via a different mechanism than its previously described role in picornavirus infection. ACBD3 was enriched at modified ERES-Golgi contact sites to support virus replication. Therefore, we propose that ACBD3 promotes flavivirus replication by modifying the trafficking between the ERES and the Golgi to enable the release of new virions. ### Competing Interest Statement The authors have declared no competing interest.