oPnosDsA ib F le m lo o c le a c ti uolnesdoefdCurcoemdefrrosm ys t M em AI EaAntt ig e e st nss Understanding of the biochemical structures and molecular basis of Rh antigens is emerging rapidly. Absence of Rh antigens, as occurs in the RhnuN phenotype, compromises the integrity of red cells and cells from people with an RhnuN phenotype have been extensively studied. These studies contributed to the recognition of Rh polypeptides and some related glycoproteins [see 20,21,22]. Partial amino acid sequencing of the proteins in Bristol, Paris and Baltimore [23,24,25] led to recognition of involvement of two genes and isolation of cDNA by the Paris and Bristol workers [26,27] and cloning of the D gene [28]. One gene is responsible for the D polypeptide and another for the C and E series of antigens. However, although encoded by the same gene there is evidence that the C and E series of antigens are carried by different proteins. The molecular genetic basis of Rh antigens is discussed in another presentation. Immune precipitation using anti-D, -c, -E or R6A antibodies demonstrated the proteins which carried the Rh antigens. Two bands are co-precipitated by anti-D: one with an apparent Mr 30,000 called D30 polypeptide by the Bristol group and the other a diffuse band of 50-100 kD called the D50 polypeptide. Similar bands were observed when immune precipitation were done using anti-c, -E or R6A [see 20-22]. The D30 polypeptide was an unusual membrane protein because it was not glycosylated, the gene producing this protein and the other Rh protein were subsequently cloned. Assignment of the genes to chromosome 1p34-p36 confirmed that they are responsible for the Rh polymorphism [see 22]. The role of the Rh glycoproteins, the diffuse band of 50-1 OOkD, is not yet understood: the gene encoding the Rh glycoprotein when cloned was assigned to chromosome 6p21-qter [29].