Once these important differences were identified, we observed restriction enzyme cleavage sites at several of the differentiated sites. For example, the sequence containing the O allele-specific single nucleotide deletion can be cleaved with KpnI, whereas the sequence without the deletion can be cleaved with BstEII. In this Southern hybridization experiment, genomic DNA from the cell line cells that were used to prepare the cDNA library was cleaved with either BstEII or KpnI, electrophoresed, Southern transferred, and hybridized with the radio-labeled A transferase probe. MKN45 genomic DNA was cleaved with BstEII but not with KpnI. Conversely, half of the SW1417 genomic DNA was cleaved with BstEII and the remaining half was cleaved with KpnI, showing that this cell line is heterozygous.