HTLV-I Tax is a zinc-binding protein: role of zinc in Tax structure and function

We have examined the functional significance of the cysteine- and histidine-rich region (amino acids 22-53) of HTLV-I Tax. A modeling of this region suggests two possible overlapping zinc-finger-like motifs. Using a zinc blotting technique, we show that Tax binds zinc. An N-terminal deletion in Tax that removed this zinc-finger region abolished the ability to bind zinc. Site-directed mutagenesis was used to generate 10 separate mutations so as to discriminate between the two alternative zinc-binding structures. Each Tax mutant was studied for its ability to trans-activate the HTLV-I LTR. Five of the ten mutations inactivated trans-activation. Our results support that one of the two putative zinc fingers is an integral element of Tax structure.