Detection of the HBZ RNA transcript. (A) HBZ transcript was detected in Poly A+ RNA isolated from SLB-1 and 729.HTLV-1, but not 729 uninfected (Uninf), using standard RT-PCR. First-strand synthesis with a specific oligo designed to copy only HTLV-1 antisense RNA containing the HBZ coding sequence was performed in the presence and absence of reverse transcriptase. The 226-bp PCR product was separated on a 2% agarose gel and visualized by ethidium bromide staining. (B) Schematic representation of the complete HTLV-1 proviral genome is shown. LTRs are depicted with their U3, R, and U5 regions. The location of the viral open reading frames and the opposite-strand HBZ are indicated. The reported HBZ coding sequence has been expanded showing the transactivation domain, basic region, and leucine-zipper region, as well as the 2 HBZ truncation mutants generated for this study (HBZΔLZ and ΔHBZ).