Borf-1 protein identified as a transcriptional trans-activator of bovine foamy virus

Bovine foamy virus (BFV), a member of the spumavirus subfamily of retroviru ses, contains two open reading frames (ORF-1 and ORF-2) in addition to the genes coding for gag, pol and env. Borf-1 protein, encoded by BFV ORF-1, is identified as a transcriptional trans-activator, which augments gene expre ssion directed by the viral long terminal repeat (LTR). Further investigati ons in transient expression assays reveal that the Borf-1 responsive elemen ts are located in the U3 domain of the LTR, upstream from position -140 (+1 represents the transcription initiation site), and the BFV RU5 region has an inhibitory effect in LTR-directed gene expression.