Sterility of Drosophila with mutations in the bloom syndrome gene - Complementation by Ku70

The Drosophila Dmblm locus is a homolog of the human Bloom syndrome gene, w hich encodes a helicase of the RECQ family. We show that Dmblm is identical to mus309, a locus originally identified in a mutagen-sensitivity screen. One mus309 allele, which carries a stop codon between two of the helicase m otifs, causes partial male sterility and complete female sterility. Mutant males produce an excess of XY sperm and nullo sperm, consistent with a high frequency of nondisjunction and/or chromosome loss. These phenotypes of mu s309 suggest that Dmblm functions in DNA double-strand break repair. The mu tant Dmblm phenotypes were partially rescued by an extra copy of the DNA re pair gene Ku70, indicating that the two genes functionally interact in vivo .