Transactivator (Tat) of bovine immunodeficiency virus (BIV) is a virus encoded regulatory protein, which activates gene expression directed by BIV long terminal repeat (LTR), and plays an important role in BIV replicative cycle. With methods of fusion protein expression and deletion mutation, a set of BIV Tat deletion mutants was constructed, and co transfected into FBL cells with BIV LTR. Using luciferase gene as a reporter, the function of BIV Tat mutants was detected and it showed that: 17/96 aa region of BIV Tat peptide contains full activity; auxiliary amino acids exist in N terminal 17/34 aa region; Cys rich region and basic region are essential to BIV Tat activity. Computer prediction of BIV Tat secondary structure was showed, and mechanism how it functions was analyzed.
Two promoters, LTR (long terminal repeat) and IP (internal promoter), exist in genomes of foamy viruses. Cell transfection and transient expression assay demonstrated that: the basal activity of BFV (bovine foamy virus) IP is much higher than that of BFV LTR; transactivator of BFV—Borf 1, which activates gene expression directed by BFV LTR, also functions on BFV IP with an activation fold higher than that on LTR. The results suggest that BFV IP and LTR may regulate viral gene expression by different mechanisms, and that Borf 1 may stimulate BFV IP and LTR in different ways. In addition, an in vivo DNA competition assay demonstrated that a common transcription factor may be involved in both mechanisms of the two promoters.
