The top panel shows a schematic of the HTLV-1 proviral genome, and the positions of the pX domain (nucleotides 6619-8281), and the vCTCF-BS. Positions of sense-strand spliced tax and p12 transcripts and the predominant antisense hbz transcript are depicted. The bottom panel shows the consensus CTCF binding sequence, and the adjacent nucleotide sequence in wild type HTLV-1. A control virus was constructed with a termination codon in p12 (blue) in place of alanine residue 77, designated HTLV-1p12Stop. A mutant virus was constructed with mutations (red) in the vCTCF-BS, as well as the p12 termination codon, designated HTLV-1ΔCTCF. The positions of mutations introduced in the sense reading frame of p12 and antisense reading frame of HBZ are shown at the bottom.