Isolation of a porcine UDP-GalNAc transferase cDNA mapping to the region of the blood group EAA locus on pig chromosome 1

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In our studies of the genes constituting the porcine A0 blood group system, we have characterized a cDNA, encoding an α (1,3)N-acetylgalactosaminyltransferase, that putatively represents the blood group A transferase gene. The cDNA has a 1095-bp open reading frame and shares 76.9% nucleotide and 66.7% amino acid identity with the human ABO gene. Using a somatic cell hybrid panel, the cDNA was assigned to the q arm of pig chromosome 1, in the region of the erythrocyte antigen A locus (EAA), which represents the porcine blood group A transferase gene. The RNA corresponding to our cDNA was expressed in the small intestinal mucosae of pigs possessing EAA activity, whereas expression was absent in animals lacking this blood group antigen. The UDP-N-acetylgalactosamine (UDP-GalNAc) transferase activity of the gene product, expressed in Chinese hamster ovary (CHO) cells, was specific for the acceptor fucosyl-α (1,2)galactopyranoside; the enzyme did not use phenyl-β-D-galactopyranoside (phenyl-β-D-Gal) as an acceptor. Because the α (1,3)GalNAc transferase gene product requires an α (1,2)fucosylated acceptor for UDP-GalNAc transferase activity, the α (1,2)fucosyltransferase gene product is necessary for the functioning of the α (1,3)GalNAc transferase gene product. This mechanism underlies the epistatic effect of the porcine S locus on expression of the blood group A antigen.Abbreviations: CDS: coding sequence; CHO: Chinese Hamster Ovary;EAA: erythrocyte antigen A; FCS: foetal calf serum; Fuc α (1,2)Gal: fucosyl-α (1,2)galactopyranoside; Gal: galactopyranoside; GGTA1: Gal α (1,3)Gal transferase; PCR: polymerase chain reaction; phenyl-β-D-Gal: phenyl-β-D-galactopyranoside; R: Gal β 1-4Glcβ1-1Cer; UDP-GalNAc: uridine diphosphate N-acetylgalactosamine

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