Predicted membrane topology and amino acid sequences of mutant Rh polypeptide species encoded by SDM constructs. This figure depicts the hypothetical membrane orientation of the Rh D polypeptide (large central panel) in which predicted externalized amino acids are numbered. The wild-type Rh D protein is then compared with SDM mutants that were derived initially from a cDNA encoding an Rh cE cDNA. The mutants were generated by inverse PCR using mutagenic primers, and the predicted extracellular positions of the targeted, Rh D-specific amino acids are shown as solid circles on each of the 7 different mutants. The polymorphic amino acid residues that differentiate the Rh D and Rh CcEe are shown as solid and open circles, respectively, with the single letter amino acid code inside each circle.