Fig. 4. The region encompassing a rearranged Vβ8.1DJ exon and flanking intron sequences is essential for strong down-regulation in response to nonsense codons. (A) H– and HC+ are TCR-β constructs that lack the VDJ exon and adjacent intron sequences. H– lacks a PTC, whereas HC+ contains a single nucleotide mutation that creates a PTC in the exon shown. AC+ is a full-length TCR-β construct identical to A– in Figure 1 except that it contains a single nucleotide mutation that creates a PTC in the exon shown. (B) Transfection, northern blot analysis and quantification were performed as in Figure 2. Comparable results were obtained in two independent transfection experiments.