Synthesis of functional bovine leukemia virus (BLV) p34tax protein by recombinant baculoviruses.

The bovine leukemia virus (BLV) p34tax (also called tat, p34, XLOR gene product) is a 34-kDa polypeptide encoded in the 3'-terminal region of the virus. This protein is responsible for positive transcriptional trans-activation of promoter elements located within the BLV long-terminal repeat. We introduced the protein-coding region of BLV p34tax into the genome of the baculovirus Autographa californica nuclear polyhedrosis virus. After infection of the insect Spodoptera frugiperda (SF9) cell line, this recombinant strain of baculovirus produced approximately 100 to 150 mg of p34tax per 2 X 10(9) cells. This protein, when introduced into mammalian fibroblasts by using a cell-to-cell fusion technique, functionally trans-activated the BLV long-terminal repeat. Analysis of 32P-labeled proteins of SF9 cells expressing BLV tax by two-dimensional gel electrophoresis indicated that the BLV p34tax was phosphorylated.