Antisense oligonucleotide inhibition of bovine leukemia virus tax expression in a cell-free system.

Tax, the trans-activating protein of bovine leukemia virus, stimulates the long terminal repeat to promote viral transcription and also activates cellular genes that may be involved in tumorigenesis. To study Tax regulation, we identified antisense oligodeoxynucleotides that inhibit tax translation in rabbit reticulocyte lysate. Two antisense oligonucleotides directed toward the 5' end of tax RNA inhibited translation by 59% and 45%, when compared to the effect of a random sequence oligonucleotide. This inhibitory effect was independent of RNase H. In contrast, antisense directed at the middle of the tax RNA inhibited by only 12%, but, in the presence of RNase H, inhibited 38%. An antisense oligonucleotide directed at the 3' portion of tax RNA was not inhibitory and, in fact, stimulated translation. Identification of these inhibitory antisense sequences may allow elucidation of the biological role of Tax in BLV-persistent lymphocytosis and tumorigenesis.