A novel HLA-DQB1 allele: Evidence for gene conversion event promoted by ?-like sequence at DQB1 locus

The genetic mechanism of MHC polymorphism generation is a controversial issue and has been supposed to vary from locus to locus (1,2). Recom- bination mechanisms (gene duplication, gene con- version, inter-allelic/inter-locus sequence ex- change) and point mutations are thought to have played different roles during the evolution of the various HLA class I1 loci (3-10). In this respect, recombination events promoted by conserved x- like putative recombination signals, found in HLA- DRBl and -DPBI genes between the P-sheet and a-helix domains, are believed to have significantly contributed to polymorphism generation at these loci (6, 9, 10). In contrast, the fact that X-like sequences have not been observed at the DQBl locus has been put forward to explain why recom- bination-like events are less frequently seen at this locus (1,4,5) where point mutations are considered to have played the major role in the polymorphism generation. In fact, very few examples of gene con- version or segmental transfer events have been hy- pothesized for the DQBl locus (3, 4).