PCR amplification of exon 2 of p16/INK4a (top) and p15/INK4b (middle). BL2 (lane 3) and BL28 (lane 5) had homozygous deletion of exon 2 of both p16/INK4a and p15/INK4b, whereas Ew36 (lane 7) had homozygous deletion of p16/INK4a exon 2 but retained p15/INK4b exon 2. The expected p16/INK4a and p15/INK4b PCR products were obtained from genomic DNA from all primary BL biopsies indicated in Table 1. Two examples, MK and TO, are shown (lanes 1 and 2). Lanes 3 to 10, BL lines; lane 11, LCL. DNA integrity was confirmed using primers specific for GAPDH exon 8 (bottom).