Alignment of amino acid sequences of Tax and Rex proteins of BLV isolates. In (A) the alignment of Tax sequences is shown. The region between amino acids 240 and 265, in which missense mutations influence the transactivation activity of the Tax protein  is shown in light blue. A putative zinc finger domain is shown in grey, a leucine-rich activation domain in yellow and sites of phosphorylation are indicated in red. Position 303, where a previously described substitution E303K gave rise to a replication-deficient virus  is shown in green. Positions where substitutions have been previously reported to have an effect on transactivation activity are shown in bold. In (B) alignment of Rex sequences is shown. Nuclear export signal (NES) is shown in yellow and the nuclear localization signal (NLS) is shown in green. The rest is the same as Figure 1.