Schematic representation of spliced transcripts of HTLV-1. ORFs are represented by open boxes. Location of ΔPstI introduced in ACH.p12^I is indicated and corresponds to the splice acceptor for exon 3 of the ORF I message. Primers used in PCR and RT-PCR are indicated above the full-length provirus. Numbers correspond to nucleotide positions with respect to the ACH clone.19