The bovine immunodeficiency virus: cloning of a tat/rev cDNA encoding a novel Tat protein with enhanced transactivation activity

Summary.

Previous studies have shown that BIV may encode two types of Tat proteins of 103 and 108 amino acids, respectively. Here, we report the characterization of a new BIV Tat protein (Tat236) derived from a tat/rev cDNA. The tat/rev cDNA was obtained by reverse transcription-PCR from RNA extracted from cells infected with BIV. BIV was rescued by cell co-cultivation from the spleen of rabbits exposed for 3 years to the R29 isolate of BIV. Sequence analysis indicated that BIV Tat236 contains the first 98 amino acids of Tat103 and the 3′ end 138 amino acids of Rev. Reporter gene assays indicated that transactivation of BIV long terminal repeat (LTR) by Tat236 is higher than by the original BIV Tat proteins in several cell types. By using overlapping deletion mutants, evidence was given that the predicted basic domain of Rev within Tat236 plays a major role in the observed enhanced transactivation activity of the protein. However, the intact functional domain of the original BIV Tat is required for efficient transactivation. This is the first report of a hybrid Tat protein from BIV or any lentiviruses that shows higher transactivation than the original transactivator Tat proteins.