(a) Trace diagrams of DNA sequencing of the PCR amplification products of healthy (top row) and diseased VSM cells (bottom row) using an antisense primer composed of nucleotides 2923–2939 (z34815). A boundary with the sequence of invariant exon 20 is marked by a vertical dotted line. (b) Evidence that the AvrII-sensitive exon 22 isoform of is expressed only in proliferating VSM cells. Primary aortic cells were grown to confluent monolayer in 5% serum before serum-deprivation for 5 days (lanes 1 and 2). Then, the cells were replated at low density in 5% serum for 3-4 days (lanes 3 and 4). Total RNA was isolated, and exon 21/22 isoforms were identified by RT-PCR and AvrII restriction analysis (lanes 2 and 4).