In particular strain of Drosophila melnogaster, hobo transposable elements in the X chromosome are responsible for a high rate of mutations, and most of the mutations are associated with chromosome rearrangements. Two hobo elements at a time are involved in the production of rearrangements, and our results suggest that the type of rearrangements produced is determined by the orientation of the elements--deleting the region marked by two elements in the same orientation and inverting the region flanked by two elements in opposite orientation. Also, one the hobo elements in the X chromosome is more active (active element) than the others (passive elements) in rearrangement formation. We propose to test these ideas by inserting the cloned hobo elements that can be mobilized by the P transposase into a strain of the fly with colorless eyes. The cloned hobo element is linked to a modified fly eye-color-gene, so emergence of flies with pigmented eyes will signal the insertion of the cloned hobo element. Therefore, the inserted hobo sequence can be transposed to a desired X-linked site by introducing a P transposase source and then eliminating it with another cross. The modified eye-color-gene is known for its sensitivity to the neighboring DNA sequences. For this reason, changes in the eye color of the transformed flies may indicate the structural change of the chromosome associated with the relocation of the inserted hobo element. The rearranged chromosomes detected in this manner will be analyzed by cytogenetic and molecular methods. The cytogenetic analyses include in situ hybridization of rearranged and pre-rearranged chromosomes with a set of appropriate probes. A sample of DNA sequences representing the rearrangement breakpoints will be cloned for molecular analyses to determine the orientation of the hobo element in each of the rearrangement breakpoints. The activities of the inserted active hobo element will also be compared with those of the inserted passive elements. Information resulting from this study will enhance our understanding of the many ways whereby DNA structure can be modified and thereby modify gene expression.***
