Molecular analysis of blood group Rh transcripts from a r(G)r variant

The Rh blood group antigens D, Cc and Ee are encoded by two related genes, RHD and RHCE, The RhG antigen (Rh12) is associated with the expression of RhC and/or RhD, except in rare variant red cells, Here we have determined the molecular basis of G expression in the absence of D and C in the r(G)r phenotype. Nucleotide sequence analysis revealed that the r(G) allele resulted either from a segmental DNA exchange between part of exon 2 of the RHce gene and the equivalent region of the RHCE or RRD genes or from a crossing over between positions nt150 and nt178 of the RHce and RHCe genes. The predicted protein encoded by the hybrid r(G) gene (c-C-e or c-D-e) carries Ile60, Ser68 and Ser103 (as C and D polypeptides); any of these positions appear to be critical in the formation of the G antigen, In addition, Cys16 was found to be important in the phenotypic expression of C.