Identification of a Novel Post-transcriptional Transactivator from the Equine Infectious Anemia Virus.

All lentiviruses encode a post-transcriptional transactivator, Rev, which mediates the export of viral mRNA from the nucleus to the cytoplasm and which is required for viral gene expression and viral replication. In the current study, we demonstrate that equine infectious anemia virus (EIAV), an equine lentivirus, encodes a second post-transcriptional transactivator that we designate Grev. Grev is encoded by a novel transcript with a single splicing event that was identified using reverse transcription-PCR (RT-PCR) and RNA-seq in EIAV-infected horse tissues and cells. Grev is about 18 kDa in size, comprises the first 18 amino acids (aa) of Gag protein together with the last 82 aa of Rev, and was detected in EIAV-infected cells. Similar to Rev, Grev is localized to the nucleus, and both are able to mediate the expression of Mat (a recently identified viral protein of unknown function from EIAV), but Rev can mediate the expression of EIAV Gag/Pol, while Grev cannot. We also demonstrate that Grev, similar to Rev, specifically binds to rev-responsive element 2 (RRE-2, located in the first exon of mat mRNAs) to promote nuclear export of mat mRNA via the chromosome region maintenance 1 (CRM1) pathway. However, unlike Rev, whose function depends on its multimerization, we could not detect multimerization of Grev using coimmunoprecipitation (co-IP) or bimolecular fluorescence complementation (BiFC) assays. Together, these data suggest that EIAV encodes two post-transcriptional transactivators, Rev and Grev, with similar, but not identical, functions.