Figure 3. Alignment of RT-PCR products for the excised inner intron.

Non-linear excised forms of the inner intron were detected via an outward pointing PCR on cDNA generated with a single outward pointing primer (primer 2). Gaps in the alignment were inserted for clarity. The top panel shows a scheme of the whole twintron as described in Figure 1. All sequencing products showed the inner intron excised as a true circle, not as a lariat, despite the presence of a canonical bulging A (alignment position 13). An additional inserted C (position 21) between the two ends of the intron hints at a 2′–5′ ligation point.