The Rh blood group system plays a major role in immune and nonimmune hemolytic states. Although an Rh cDNA has been previously cloned, there is no information on which Rh antigenic protein it encodes. Using polymerase chain reaction (PCR) amplification, we have identified this original Rh clone, here designated Rh21, and an additional Rh cDNA clone, Rh13, that is 96% nucleotide- and 92% amino acid-identical to Rh21, with the substitutions scattered throughout the sequence. A molecular genetic approach was used to match this Rh clone with an Rh specificity. The mRNA transcript for Rh13 was present in reticulocytes from RhD-positive individuals, but was absent from the reticulocytes of RhD-negative individuals. Using conventional screening of genomic libraries, as well as PCR cloning, partial genomic clones for these two Rh cDNAs were obtained. Based on PCR analysis and Southern blots, the Rh21 gene was present in all individuals, but an intact Rh13 gene was only present in RhD-positive and not RhD-negative individuals. Thus, by correlating the presence of Rh mRNA and gene sequences with individual Rh phenotypes, we were able to establish that the new Rh13 cDNA clone represents the RhD protein.

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