(A) Nucleotide sequence of the CpG island in exon 1. Putative methylation sites of exon 1 are illustrated. CG sequences are bold, and the HpaII/MspI sites are underlined. Numbers above the nucleotide sequence are based on the cDNA sequence in the European Molecular Biology Laboratory database under the accession number Y11416EMBL. (B) Methylation status of CpG island in exon 1. Digests of 20 ng of genomic DNA with either HpaII orMspI were amplified by PCR using primers that amplify the entire exon 1 DNA (77 bp). U, uncut; H, HpaII; M,MspI.