INVESTIGATION OF THE RH LOCUS IN GORILLAS AND CHIMPANZEES

The human Ph blood-group system is encoded by two homologous genes, Rh D and RHCE. The RH genes in gorillas and chimpanzees were investigated to delineate the phylogeny of the human RH genes. Southern blot analy sis with an exon 7-specific probe suggested that gorillas have more th an two RH genes, as has recently been reported for chimpanzees. Exon 7 was well conserved between humans, gorillas, and chimpanzees, althoug h the exon 7 nucleotide sequences from gorillas were more similar to t he human D gene, whereas the nucleotide sequences of this exon in chim panzees were more similar to the human CE gene. The intron between exo n 4 and exon 5 is polymorphic and can be used to distinguish the human D gene from the CE gene. Nucleotide sequencing revealed that the basi s for the intron polymorphism is an Alu element in CE which is not pre sent in the D gene. Examination of gorilla and chimpanzee genomic DNA for this intron polymorphism demonstrated that the D intron was presen t in all the chimpanzees and in all but one gorilla. The CE intron was found in three of six gorillas, but in none of the seven chimpanzees. Sequence data suggested that the Alu element might have previously be en present in the chimpanzee RH genes but was eliminated by excision o r recombination. Conservation of the RhD gene was also apparent from t he complete identity between the 3'-noncoding region of the human D cD NA and a gorilla genomic clone, including an Alu element which is pres ent in both species. The data suggest that at least two RH genes were present in a common ancestor of humans, chimpanzees, and gorillas, and that additional RH gene duplication has taken place in gorillas and c himpanzees. The RhCE gene appears to have diverged more than RhD among primates. In addition, the RhD gene deletion associated with the Rh-n egative phenotype in humans seems to have occurred after speciation.