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Am J Hum Genet. 1996 Oct;59(4):825-33.

Genetic recombination at the human RH locus: a family study of the red-cell Evans phenotype reveals a transfer of exons 2-6 from the RHD to the RHCE gene.

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Lindsley F. Kimball Research Institute, New York Blood Center, NY 10021, USA.


The human RH locus appears to consist of two structural genes, D and CE, which map on the short arm p34-36 of chromosome 1 and specify a most complex system of blood-group genetic polymorphisms. Here we describe a family study of the Evans (also known as "D..") phenotype, a codominant trait associated with both qualitative and quantitative changes in D-antigen expression. A cataract-causing mutation was also inherited in this family and was apparently cotransmitted with Evans, suggesting a chromosomal linkage of these two otherwise unrelated traits. Southern blot analysis and allele-specific PCR showed the linkage of Evans with a SphI RFLP marker and the presence of a hybrid gene in the RH locus. To delineate the pattern of gene expression, the composition and structure of Rh-polypeptide transcripts were characterized by reverse transcriptase-PCR and nucleotide sequencing. This resulted in the identification of a novel Rh transcript expressed only in the Evans-positive erythroid cells. Sequence analysis showed that the transcript maintained a normal open reading frame but occurred as a CE-D-CE composite in which exons 2-6 of the CE gene were replaced by the homologous counterpart of the D gene. This hybrid gene was predicted to encode a CE-D-CE fusion protein whose surface expression correlates with the Evans phenotype. The mode and consequence of such a recombination event suggest the occurrence, in the RH locus, of a segmental DNA transfer via the mechanism of gene conversion.

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