The coding sequence of Duffy blood group gene in humans and simians: restriction fragment length polymorphism, antibody and malarial parasite specificities, and expression in nonerythroid tissues in Duffy-negative individuals.

The coding and untranslated flanking sequences of Duffy gene (FY) in humans and simians are in a single exon. The difference between the two codominant alleles, FYA and FYB, is a single change at nucleotide 306: guanidine is in FYA and adenine is in FYB. This produces a codon change that subsequently modifies the amino acid at position 43 of gpFy, the major subunit of the Duffy blood group protein complex. The glycine at this position in antigen Fya exchanges with aspartic acid in antigen Fyb. The guanidine at nucleotide 306 creates an additional Ban I restriction site in FYA. Ban I digestion of DNA-PCR amplified products of FYB and FYA yields three and four fragments, respectively. Restriction fragment length polymorphism (RFLP) studies show that Fy(a+b-) and Fy(a-b+) whites are FY homozygous, that most Fy(a-b-) blacks have FYB, and most Fy(a+b-) blacks are FYA/FYB heterozygous. In the black population a silent FYB is very common, but a silent FYA has not been found yet. On RNA blot analysis, the gpFy cDNA clone detected mRNA in the lung, spleen, and colon but not in the bone marrow of Duffy-negative individuals. Therefore, there is no null phenotype in Fy(a-b-) blacks. The gpFy homology between human and chimpanzee is 99% with a single residue change at position 116 (valine to isoleucine), whereas a 94% homology is found in squirrel and rhesus monkeys, and there is a 93% homology in aotus monkey when compared with humans. The N-terminal exocellular domain of simian gpFy helps to identify a set of amino acids critical for antibody and malarial parasite specificities.