Drosophila melanogaster mutations suppressible by the suppressor of Hairy-wing are insertions of a 7.3-kilobase mobile element.

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Abstract
Certain spontaneous mutations of Drosophila melanogaster are suppressed by su(Hw), the suppressor of Hairy-wing (3R-54.8). We find that mutations suppressible by su(Hw) result from insertions of a mobile element at the affected loci. The element, named gypsy, is approximately 7.3 kilobases long and includes 0.5-kilobase direct terminal repeats. It was first identified in DNA cloned from the bithorax chromosomal region of several Drosophila stocks carrying suppressible mutations of the bithorax complex. Cloned gypsy DNA was used as a probe to test for the association of gypsy with suppressible mutations at various other loci by hybridization in situ. Gypsy was found to be associated with 19 suppressible alleles at 10 different loci: yellow, Hairy-wing, scute, diminutive, cut, lozenge, forked, Beadex, hairy, and the bithorax complex. It was found with wild-type or nonsuppressible mutations at any of these loci. Gypsy DNA was also used as a probe to clone the element and adjacent unique DNA from the loci of some suppressible mutations. This confirmed the presence of the full-length element and also provided cloned DNA from the previously uncloned loci scute and cut. The suppressor of Hairy-wing is generally recessive and behaves as a null mutation. Thus, the disruption of normal gene function caused by the inserted gypsy element appears to require some product of the wild-type suppressor gene, su(Hw)+.