In vivo analysis of Drosophila BLM helicase function during DNA double-strand gap repair

The BLM helicase is a member of the RecQ DNA helicase family and is mutated in the cancer-prone disorder Bloom syndrome. BLM plays a role in a number of cellular processes including DNA double-strand break repair, Holliday junction dissolution, and chromosome segregation. In Drosophila melanogaster, the BLM ortholog (DmBlm) is encoded by the mus309 gene. To study the role of DmBlm in double-strand break repair, we utilized a genetic assay in which a targeted DNA double-strand gap is created through excision of a P transposable element. By recovering and molecularly analyzing individual repair products from wild-type and mus309 male pre-meiotic germline cells, we demonstrated that the DmBlm helicase is involved in homologous recombination downstream of strand invasion. This assay can be adapted to test the roles of numerous DNA metabolic factors in DNA double-strand gap repair.