FIG. 6.

Domain structure of the HTLV-1 Rex trans-activator protein. The four distinct functional regions located within the 189-aa Rex protein are indicated by boxes (see text for details). Interaction of Rex with its RxRE target sequence and nuclear-nucleolar localization of the protein are mediated by the Rex amino terminus (aa 1 to 19; hatched box). The protein activation domain, which contains a leucine-rich peptide core motif that serves as a nuclear export signal, is located in the center of the protein (aa 79 to 99; cross-hatched box). Regions involved in the multimerization of Rex are localized in both the amino-terminal and carboxy-terminal halves of the protein (aa 57 to 66 and aa 106 to 124; filled boxes). The amino acid sequences of these multimerization domains are shown as expanded sections. The Rex sequences indicated by grey boxes are dispensable for in vivo Rex function (39) and appear to serve a structural rather than a directly functional role in Rex. NLS, nuclear localization signal; NES, nuclear export signal.