Molecular Genetic Analysis of the ABO Blood Group System: 3. Ax and B(A) Alleles

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Abstract
We have employed a PCR approach to determine the nucleotide sequences of the coding region in the last two coding exons of the histo-blood group ABO genes from one Ax and one B(A) individual. Compared with A1 alleles, the Ax allele has a single nucleotide substitution (T→ A at nucleotide 646) resulting in an amino acid substitution (phenylalanine→isoleucine at amino acid 216). Compared with B alleles, the B(A) allele has two nucleotide substitutions (T→C at nt. 657 and A→G at nt. 703) resulting in an amino acid substitution (serine→glycine at aa. 235). The amino acid substitution resulting from this B(A) allele is located at the second of the four amino acid substitutions which discriminate human A and B transferases, and the amino acid residue (glycine) is identical to that of A transferase suggesting the involvement of this amino acid or its surrounding area for the recognition and/or binding of the donor nucleotide sugars.