THE CAPRINE ARTHRITIS-ENCEPHALITIS VIRUS TAT GENE IS DISPENSABLE FOR EFFICIENT VIRAL REPLICATION IN-VITRO AND IN-VIVO

Caprine arthritis encephalitis virus (CAEV) is a lentivirus closely re lated to visna virus and more distantly to other lentiviruses, such as human immunodeficiency virus. The genomes of visna virus and CAEV con tain a tat gene encoding a protein able to weakly transactivate its ow n long terminal repeat, suggesting that transactivation may be a dispe nsable function for viral replication. Three different tat gene mutant s of an infectious molecular clone of CAEV were used to study their re plication after transfection or infection of primary goat synovial mem brane cells and of blood-derived mononuclear cells or macrophages. Our results showed no difference between replication of the wild type and either the complete tat deletion mutant or the tat stop point mutant, whereas slower growth kinetics and lower levels of expression of the partial tat deletion mutant than of the wild type were obtained in the se cells. Quantitative PCR and reverse transcription-PCR analyses of t he different steps of a single replicative cycle revealed an identical pattern of retrotranscription, transcription, and viral production, w hereas time course analysis demonstrated that the intracellular level of viral genomic RNA was affected by the partial tat deletion at later time points. We then compared the infectious properties of the wild-t ype and tat mutant viruses in vivo by direct inoculation of proviral D NAs into the joints of goats. All the animals seroconverted between 27 and 70 days postinoculation. Moreover, we were able to isolate tat mu tant CAEV from blood derived macrophages that was still able to infect synovial membrane cells in vitro. This study clearly demonstrates tha t the tat gene of CAEV is dispensable for viral replication in vitro a nd in vivo.