Identification of two Rh mRNA isoforms expressed in immature erythroblasts.

Two isoforms of RhPI cDNA encoding an Rh polypeptide, RhPI-alpha and RhPI-beta, were isolated from mRNAs of immature erythroblasts cultured in a selective two-phase liquid culture system for human erythroid progenitors in peripheral blood. The RhPI-alpha and RhPI-beta cDNA clones encoded the hydrophobic membrane polypeptides of 242 and 244 amino acids which were missing in amino acid residues 227 to 383 and 212 to 384 of RhPI polypeptide, respectively. These peptide deletions produce unexpected structural properties resulting in the generation of a new open reading frame with a new stop codon caused by frameshift translations in RhPI-alpha cDNA and in the reverse orientation of topology in RhPI-beta cDNA. Both isoforms are abundantly present in immature erythroblasts, but not in mature erythroblasts. These results indicate that the two Rh-related mRNAs identified are expressed at the immature erythroblast stage on the development of erythroid series.