FIG. 2.

Schematic representation of the recombinant BLV proviruses. Based on their ability to propagate efficiently in the animal model, the recombinant proviruses were separated into two groups. The mutants which behave similarly to the wild-type pBLV344 virus include pBLV344/395 (which is a hybrid between the 344 and 395 viruses harboring most of the 395 genome linked to the tax/rex region of the 344 strain), pBLVX3C (which contains the complete X3C ORF corresponding to the 5′ end of the R3 second exon from the FLK/BLV strain), and pBLVIX (which contains a small deletion between two XbaI restriction sites at positions 6614 and 6732). Three types of attenuated viruses were characterized: pBLVDX (which contains deletions of both the R3 and G4 genes), pBLVRZ (which is isogenic to pBLVDX but contains a ribozyme directed towards the tax gene sequences), and pBLVIG4 (in which a translational stop codon was inserted into the G4 gene). The precise description of these viruses was given elsewhere (23, 24). LTR, long terminal repeat.