CHARACTERIZATION OF THE RECOMBINATION HOT-SPOT INVOLVED IN THE GENOMIC REARRANGEMENT LEADING TO THE HYBRID D-CE-D GENE IN THE D-VI PHENOTYPE

In the Caucasian population, the RH locus of RhD-positive individuals is composed of two homologous genes, RHD and RHCE, arranged in tandem but of a single gene, RHCE, in RhD-negative individuals. Many variants recently characterized carry rearranged RH genes, most often by an un idirectional segmental DNA-exchange (gene-conversion) event. In D-VI v ariants of type II, RND is a D-CE-D hybrid gene in which the DNA fragm ent carrying exons 4-6 has been replaced by the corresponding sequence s from the RHCE gene. To identify precisely and characterize the two t ransition sites, we have studied, by both PCR and sequence analysis, a genomic region between the 3' end of intron 3 and exon 7 in normal RH CE and RHD genes as well as in D-VI DNA. We show that the D-CE breakpo int is located in intron 3, within a 250-bp fragment comprising an Alu S sequence, and that the CE-D breakpoint lies within a 39-bp fragment in intron 6. This Alu S sequence (and the 100-bp region immediately d ownstream) most likely defines a recombination hot spot, since there l ies also the 5' breakpoint of different rearrangement events leading t o D-CE and CE-D transitions in hybrid D-VI,DFR and Dc-,R(N) gene compl exes, respectively.