Expression studies of the G836 or A836 alleles. cDNA was prepared from RNA extracts of blood samples and amplified by PCR using primers D and C. The 101-bp PCR products were digested withMnlI, and the fragments were analyzed on agarose gel. Products containing the G836 sequence are cut into 22- and 79-bp fragments, whereas those with A836 are uncut. After digestion, only the 101-bp fragment was detected with Y.T., indicating that only the allele carrying the A836 mutation is transcriptionally expressed. In contrast, both the 101- and 79-bp fragments were present in A.H. and M.P., indicating that both A836 and G836 are expressed.