Helicases play essential roles in virtually all DNA metabolic pathways. One important helicase family is the RecQ type, named for similarity to E. coli RecQ helicase. RecQ helicases are conserved between prokaryotes and eukaryotes, and a multi-gene family exists in metazoa. In humans, five members of this family are currently known. Three have been found to be associated with hereditary disorders (Werner syndrome, Bloom syndrome, and Rothmund-Thomson syndrome). Although these disorders are clinically dissimilar, they share is a predisposition to cancers and a cellular phenotype of genome instability.
RecQ helicases are clearly important in cellular metabolism. Their precise functions, however, are largely unclear. We are addressing the functions of the three Drosophila RecQ helicases:
DmBlm is the product of the mus309 gene, and is the Drosophila ortholog of Blm, which is mutated in Bloom Syndrome. Patients with Bloom syndrome have short stature, immune system deficiencies, skin and skeletal abnormalities, and a extreme predisposition to cancers of all types. Mutations in mus309 confer hypersensitivity to ionizing radiation and other DNA damaging agents. We recently showed that DmBlm plays an important function in repairing DNA double-strand breaks by the synthesis-dependent strand annealing (SDSA) pathway.
RecQ5 is interesting in that it exists in three different isoforms, generated by alternative splicing. This feature is conserved in human RecQ5. We used targeted gene replacement to knock out Drosophila RecQ5, but so far the mutants have no discernable phenotype. Our collaborators across the hall, Zeynep Ozsoy and Steve Matson, have purified biochemically characterized the small isoform of Drosophila RecQ5.
RecQ4 is the ortholog of human RecQ4, which is mutated in Rothman-Thomson syndrome. We are currently using targeted gene replacement to knock out this gene.
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