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To seek an alternative model for studies of theRh protein complex, we isolated by homology cloning andcharacterized the mouse Rhced and Rhaggenes, which are homologous to the human RH andRHAG genes,respectively. Rhced encodes a glycoprotein of418 amino acids which occurs as a composite of human RhDand RhCE with 60% identity and 74% similarity. Rhagencodes a glycoprotein of 438 amino acids thatshares 79% identity and 87% similarity to humanRh50. However, Rhag has an elongated C terminus and fourN-glycosylation sites clustered on exoloop 1. Hydropathyplots suggest that Rhl1 and Rhag each spanthe lipid bilayer 12 times, with N and Ctermini facing the cytoplasm. Rhced and Rhag are bothspecified by 10 exons and bear a similar exon/intronstructure, but their major transcription start sites aremapped at –17A and –27A. Northernanalysis revealed coexpression of Rhced and Rhag from11-day embryos throughout adult life in erythroidtissues. Southern blotting and linkage analysis showedthat Rhced and Rhag are single-copygenes localized to chromosomes 4 and 17, respectively;they are paralogous to one another but orthologous tohuman RH and RHAG. The resultstogether predate the occurrence and signifya conserved function of the erythroid-specificRh membrane structures.