Molecular lesions associated with white gene mutations induced by I-R hybrid dysgenesis in Drosophila melanogaster

We have identified molecular lesions associated with six mutations, w^IR2 and w^IR4-8, of the white gene of Drosophila melanogaster. These mutations arose in flies subject to I-R hybrid dysgenesis. Four of the mutations give rise to coloured eyes and are associated with insertions of 5.4-kb elements indistinguishable from the I factor controlling I-R dysgenesis. The insertion associated with w^IR4 is at a site which, within the resolution of these experiments, is identical to that of two previously studied I factors. This appears to be a hot-spot for I factor insertion. We have compared the sites of these insertions with sequences complementary to white gene mRNA identified by Pirrotta and Bröckl. The hot-spot is in the fourth intron. The insertion carried by w^IR5 is either within, or just beyond, the last exon. The insertion carried by w^IR6 is near the junction of the first exon and first intron. The w^IR2 mutation is a derivative of w¹. It contains an insertion of I factor DNA within, or immediately adjacent to, the F-like element associated with w¹, and results in restoration of some eye colour. This insertion is just upstream of the start of the white mRNA. Mutations w^IR7 and w^IR8 are deletions removing mRNA coding sequences. Both determine a bleached white phenotype.