Sequence analysis of the boundaries of the tandem duplication from the white-ivory mutant of Drosophila melanogaster and two chemically induced revertants

We have previously shown that revertants obtained from the white-ivory, mut ants of Drosophila melanogaster, both spontaneous and induced, have lost a DNA fragment of 2.9 kb that is duplicated in tandem in the white-ivory muta tion. To prove the accuracy of the deletion in revertants obtained after tr eatment with alkylating agents, we have sequenced DNA fragments previously amplified by PCR. These fragments correspond to the ends of the remaining 2 .9 kb copy of these revertants and the internal region of the junction of b oth copies, which constitutes the duplication in the white-ivory mutant. Th ese sequences are compared with those from white-ivory mutants. Our results show slight differences from the published sequence of the white-ivory mut ation and with the wild-type sequence of the white locus. The sequences of the two revertants analysed show that excision of the duplicated fragment i s very precise. We hypothesize the mechanism of excision in terms of intrac hromosomal recombination induced by double-strand break repair after treatm ent with alkylating agents.