Southern blot hybridization of RT-PCR products. Oligo-dT primed reticulocyte RNA was used for PCR with primers R-4 and R-5 flanking exon 7 of the R-PK cDNA. Normal R-PK cDNA is 336 bp long, which includes 25, 271, and 40 bp cDNA sequences of exon 6, 7, and 8. If the 96 bases of the seventh intervening sequence are retained, the aberrant cDNA becomes 432 bp long. Oligonucleotide EX-7 hybridized with exon 7 (lane 1, PK Kowloon, lane 2; control), and IVS-7 hybridized with intron 7 (lane 3, PK Kowloon, lane 4; control).