COMPLEX RECOMBINATION EVENTS AT THE HYPERMUTABLE MINISATELLITE CEB1 (D2S90)

Some minisatellite structures are the site of high rates of DNA recombination in non-pathological situations, with an excess of motif insertion events and a locus-dependent sex-specific mutation bias. We previously reported the cloning of the hypermutable minisatellite locus CEB1 (D2S90), remarkable for its 13% mutation rate in the male germline (compared to similar to 0.4% in female). We have sought to analyse the mechanisms underlying the addition or deletion of motifs at this locus using the minisatellite variant repeat mapping technique. This is possible with a high precision due to the extreme sequence polymorphism seen between different motifs. No crossing-over event was observed among 38 informative neomutations. Four of the 19 informative mutant alleles with an addition of motifs are interallelic events, the others are intra-allelic. Overall, the insertion and deletion mutations are spread along the alleles, although the subset of interallelic events shows clustering towards the analysed end. The apparently complex recombination events observed can all be interpreted as a succession of elementary duplications-deletions of inter- as well as intra-chromosomal origin, suggesting a model in which sister chromatid as well as conversion-like exchanges are involved in these mutation processes.