Fig. 1.

Rh topology in the RBC membrane. The protein is assumed to possess 12 transmembranous segments, 6 extracellular loops, and 5 intracellular loops. Both the C- and N-terminal ends of the protein are intracellular. Each amino acid is depicted by a circle; black circles indicate positions that differ between RhD and RhCE in all frequent alleles, grey circles indicate positions that differ between RhD and RhCE only in some alleles. Most differences are located in transmembranous or intracellular segments; among the extracellular loops, only loops 3, 4, and 6 differ between RhD and RhCE. The latter fact is most important for D antigen expression and is discussed in detail in the text.