The vif gene is essential for efficient replication of caprine arthritis encephalitis virus in goat synovial membrane cells and affects the late steps of the virus replication cycle.

Complex retrovirus genomes contain a variable number of accessory genes, among which is the vif gene. We investigated in vitro the role of the vif gene of caprine arthritis encephalitis virus (CAEV) by studying the phenotype of five vif mutants after infection of primary goat synovial membrane (GSM) cells and blood-derived monocytes/macrophages. Any deletion introduced into the vif gene resulted in slow and low viral replication and production of virions with an infectious titer lower than that of wild-type viral particles. The wild-type phenotype could be restored by the trans expression of the vif gene in a complementation assay. Quantitative PCR and reverse transcription-PCR analyses were performed in order to determine which stage of the replicative cycle was impaired by the vif deletion. Our results demonstrated that CAEV Vif did not act at the level of reverse transcription or transcription but rather at the late stage of virus formation and/or release, as lower amounts of virus were produced after a single replicative cycle. The vif-deleted CAEV produced after 24 h of infection was still able to infect GSM cells, indicating that the vif gene is not essential for virus infectivity but is required for efficient virus production.