Once cDNA clones encoding potential A transferase were identified, we performed Northern hybridization experiments using RNAs prepared from cell line cells that exhibited different ABO phenotypes. The results showed that homologous messages were present in cell line cells with different ABO phenotypes. Therefore, we attempted to isolate cDNA clones containing homologous sequences from those cell line cells. (The ABO phenotypes of the cell line cells and the blood types of the patients from whom the cell lines were derived are shown in the parentheses. For example, MKN45 cells express A antigens, but the blood type of the patient was unknown, while SW48 cells express A and B antigens and were derived from a blood type AB patient).