Frameshift mutation in exon 2. (A) RT-PCR analysis of exon 2 sequence in tumor no. 3 (see Table 1 for primers). PCR products were resolved on a 10% polyacrylamide gel. The PCR product derived from the tumor is slightly smaller than that from U266. (B) Sequence chromatogram of cDNA derived from tumor no. 3 showed 4-bp deletion, which results in frameshift and premature translation termination. Note absence of expression of a normal PRDM1 allele in both (A) and (B).