Abstract
Expression of the structural proteins of human T-cell leukemia virus type I is dependent upon the interaction of the viral Rex trans activator with its highly structured cis-acting RNA target sequence, the 254-nucleotide Rex-response element. Nucleotides critical for Rex binding in vitro have been mapped by modification interference analysis to a discrete 12-nucleotide RNA sequence that is predicted to form a stem-bulge-stem structure. This minimal RNA binding site was sufficient to mediate specific Rex binding in vitro when analyzed in the context of a short RNA probe. The critical importance of this short RNA sequence in mediating Rex function in vivo is supported by its complete conservation among all primate T-cell leukemia virus isolates.