Cloning and expression of the histo-blood group PkUDP-galactose:: Galβ1-4Glcβ1-Cer α1,4-galactosyltransferase -: Molecular genetic basis of the p phenotype

The molecular genetic basis of the P histo-blood group system has eluded characterization despite extensive studies of the biosynthesis of the P-1, P, and P-k glycolipids. The main controversy has been whether a single or two distinct UDP-Gal:Gal beta 1-R 4-alpha-galactosyltransferases catalyze the syntheses of the structurally related P-1 and P-k antigens. The P-1 polymorphism is linked to 22q11.3-ter. Data base searches with the coding region of an alpha 4GlcNAc-transferase identified a novel homologous gene at 22q13.2 designated alpha 4Gal-T1. Expression of full coding constructs of alpha 4Gal-T1 in insect cells revealed it encoded P-k but not P-1 synthase activity. Northern analysis showed expression of the transcript correlating with pk synthase activity and antigen expression in human B cell lines. Transfection of P-k-negative Namalwa cells with alpha 4Gal-T1 resulted in strong pk expression. A single homozygous missense mutation, M183K, was found in six Swedish individuals of the rare p phenotype, confirming that alpha 4Gal-T1 represented the P-k gene. Sequence analysis of the coding region of alpha 4Gal-T1 in P-1+/- individuals did not reveal polymorphisms correlating with P1P2 typing.