Sequences of the gypsy transposon of Drosophila necessary for its effects on adjacent genes

The Drosophila melanogaster transposon gypsy is the cause of numerous spontaneous mutations, most of which are suppressible by mutations in the suppressor of Hairy wing [su(Hw)] locus. We have examined the phenotype of four revertants of the gypsy element-induced mutation bithoraxoid1 (bxd1) and determined the molecular basis of these reversions. All four revertants have undergone deletions within the gypsy element. The altered gypsy element from one of the partial revertants has been cloned. It has a deletion of only 109 base pairs near the 5' end of the gypsy transcription unit. Similar deletion gypsy elements exist elsewhere in the Drosophila genome. We discuss a mechanism by which the 109-base segment might affect the bxd phenotype.