Gene deletions by ends-in targeting in Drosophila melanogaster.

Following the advent of a gene targeting technique in Drosophila, different methods have been developed to modify the Drosophila genome. The initial demonstration of gene targeting in flies used an ends-in method, which generates a duplication of the target locus. The duplicated locus can then be efficiently reduced to a single copy by generating a double-strand break between the duplicated segments. This method has been used to knock out target genes by introducing point mutations. A derivative of this method is reported here. By using different homologous regions for the targeting and reduction steps, a complete deletion of the target gene can be generated to produce a definitive null allele. The breakpoints of the deletion can be precisely controlled. Unlike ends-out targeting, this method does not leave exogenous sequence at the deleted locus. Three endogenous genes, Sir2, Sirt2, and p53 have been successfully deleted using this method.