RAB1A promotes Vaccinia virus replication by facilitating the production of intracellular enveloped virions

•Characterisation of the role of the small GTPase RAB1A in VACV replication.•RAB1A is not required for production of the primary virion form (IMV).•RAB1A is required for production of processed virion forms (IEVs, CEVs and EEVs).•Consistent with known role of RAB1A in ER to Golgi transport.

Vaccinia virus (VACV) is a large double-stranded DNA virus with a complex cytoplasmic replication cycle that exploits numerous cellular proteins. This work characterises the role of a proviral cellular protein, the small GTPase RAB1A, in VACV replication. Using siRNA, we identified RAB1A as required for the production of extracellular enveloped virions (EEVs), but not intracellular mature virions (IMVs). Immunofluorescence and electron microscopy further refined the role of RAB1A as facilitating the wrapping of IMVs to become intracellular enveloped virions (IEVs). This is consistent with the known function of RAB1A in maintenance of ER to Golgi transport. VACV can therefore be added to the growing list of viruses which require RAB1A for optimal replication, highlighting this protein as a broadly proviral host factor.