Models of the structure of D antigen variants DVI type I and DAR. (A) DVI type I polypeptide. Residues encoded by exons 4 and 5 (which are replaced by CE sequence in DVI type I) are shown in cyan. Residues in exons 4 and 5 that differ from those in normal D polypeptide are shown as blue spheres. (B) DAR polypeptide. Residues that distinguish DAR from normal D polypeptide are shown as red spheres. In this model DAR-associated residues are not surface exposed and not visible on the molecular surface.