The 3′ region of bovine leukemia virus genome encodes a trans‐activator protein

The genome of bovine leukemia virus (BLV) contains several overlapping, long open reading frames 3′ to the envelope gene. Experiments presented here show that the cDNA encompassing the X region open reading frames encodes a trans‐activator function capable of increasing the level of gene expression directed by the BLV long terminal repeat sequences. This study provides further evidence of the structural and functional similarities of the bovine leukemia virus and the human T lymphotropic viruses, HTLV‐I and HTLV‐II.