INVOLVEMENT OF SER103 OF THE RH POLYPEPTIDES IN G-EPITOPE FORMATION

Background: Almost all red cells that carry D and/or C antigens also e xpress the G antigen (Rh12). A study was conducted on the molecular ba ckground of the G epitope. Study Design and Methods: Two unrelated don ors with the rare ccDEe, G- phenotype and one donor with the ccEe, Gphenotype were studied. Genomic DNA and cDNA of these donors were stud ied with polymerase chain reaction, Southern blot, and sequence analys is, with special focus on exon 2, because it is only in this exon that there are supposed to be similarities between RHD and the RHC allele, but not between RHD and the RHc allele. Results: In both ccDEe, G- do nors, a nucleotide substitution was found in exon 2 of RHD; T307 was r eplaced by C307, which predicted a Ser-->Pro substitution at amino aci d position 103 of the D polypeptide. The ccEe, G+ donor carried the co mplete exon 2 of RHD. Moreover, despite the absence of all known D epi topes, this donor also carried RHD characteristics in exons 1 to 3 and exon 9 and further downstream. Conclusion: Ser103, encoded by exon 2 of the RH genes, is involved in G epitope formation.