2 SPECIES OF REV PROTEINS, WITH DISTINCT N-TERMINI, ARE EXPRESSED BY CAPRINE ARTHRITIS-ENCEPHALITIS VIRUS

Several cDNA clones representing alternatively spliced Rev-specific tr anscripts were isolated from a cDNA library prepared from Himalayan ta hr cells infected with caprine arthritis encephalitis virus (CAEV). We previously characterized two rev-like cDNA species, d1 and d2, and a tat e1 cDNA containing the rev coding sequence downstream to the tat. In these cDNAs, the rev coding domain derives its amino terminus from the N terminus of env, which is spliced the 3' open reading frame enco ding the putative Rev protein. In this study, we report the genetic st ructure of a fourth rev-like cDNA (designated g1), which lacks the 5' env-derived sequences. All of these rev transcripts, including cDNA g1 , increased the level of chloramphenicol acetyltransferase expression when cotransfected with a reporter plasmid containing the CAEV Rev-res ponsive element-spanning region downstream of the cat coding sequences . Western blot (immunoblot) analysis showed that each transfected cDNA species gave rise to a 16-kDa protein lacking env-encoded amino-termi nal epitopes. In contrast, CAEV-infected Himalayan tahr cells expresse d only a 20-kDa protein, whose N terminus, in contrast, is derived fro m the env. Moreover only the 20-kDa protein was also detected in the m ature CAEV virions. These observations suggest that the transcripts d1 , d2, and e1 can potentially, in appropriate cellular contest, encode two Rev isoforms differing in their N termini, whereas the g1 transcri pt encodes only the 16-kDa species. Elucidation of the significance of the 16-kDa Rev protein in CAEV biology must await further studies.