Recombinants from a proviral bovine leukemia virus genome corresponding to the 3' region transactivate viral LTR in NIH3T3 and non-infected FLK cells.

Bovine leukemia virus (BLV), like human T-cell leukemia viruses, Types I and II, contains three open reading frames at the 3' end of its genome. The longest open reading frame encodes a transactivator protein which is generated by a doubly-spliced mRNA. A series of co-transfection experiments, using proviral BLV pX expression plasmids under the control of the Moloney leukemia virus LTR and the indicator plasmid containing the assayable lac Z gene under the control of BLV LTR, revealed that both NIH3T3 cells and non-infected fetal lamb kidney cells are able to express an active transactivator protein.