RT-PCR analyses of splice products generated in vivo. (A) The structures of the potential splice products A to D are illustrated at the top, with the positions and orientations of the PCR primers (see Materials and Methods) from the four primer sets depicted below. The predicted origins and sizes of the amplified fragments are given at the right. (B) Shown are examples from each series of amplified RT-PCR products visualized on ethidium bromide-stained agarose gels. The employed primer sets (#1 to #4) are listed above the lanes. Size markers are indicated at the left.