The mouse Rhl1 and Rhag genes: sequence, organization, expression, and chromosomal mapping

To seek an alternative model for studies of the Rh protein complex, we isolated by homology cloning and characterized the mouse Rhced and Rhag genes, which are homologous to the human RH and RHAG genes, respectively. Rhced encodes a glycoprotein of 418 amino acids which occurs as a composite of human RhD and RhCE with 60% identity and 74% similarity. Rhag encodes a glycoprotein of 438 amino acids that shares 79% identity and 87% similarity to human Rh50. However, Rhag has an elongated C terminus and four N-glycosylation sites clustered on exoloop 1. Hydropathy plots suggest that Rhl1 and Rhag each span the lipid bilayer 12 times, with N and C termini facing the cytoplasm. Rhced and Rhag are both specified by 10 exons and bear a similar exon/intron structure, but their major transcription start sites are mapped at -17A and -27A. Northern analysis revealed coexpression of Rhced and Rhag from 11-day embryos throughout adult life in erythroid tissues. Southern blotting and linkage analysis showed that Rhced and Rhag are single-copy genes localized to chromosomes 4 and 17, respectively; they are paralogous to one another but orthologous to human RH and RHAG. The results together predate the occurrence and signify a conserved function of the erythroid-specific Rh membrane structures.