| The cellular response to DNA damage is crucial for cell survival and genome maintenance. An accumulation of damage can lead to disease and cancer. Multiple pathways mediate the response to both exogenous damage, such as radiation, and endogenous damage that occurs during replication and DNA metabolism. These pathways include repair of the lesion, cell cycle regulation, and programmed-cell death. The orchestration of these seemingly distinct pathways is necessary to ensure accurate and efficient response to DNA damage.; In this dissertation, I addressed several questions regarding multiple components of the response to DNA damage in Drosophila melanogaster. These components include homologs of Blm (DmBlm), a RecQ helicase, and ATR (DmATR), a kinase required for the DNA damage checkpoint. Previous work demonstrated that DmBlm is required for homologous recombination repair of a DSB, and in the absence of DmBlm, repair is often associated with flanking deletions. Work presented here shows that these deletions are large and occur after strand-invasion, thereby genetically placing DmBlm at a specific step of homologous recombination repair.; Studies presented in the remainder of this dissertation focus on DmATR, which is required for the DNA damage checkpoint. I show that DmATR mutants are defective in the later steps of homologous recombination repair of a DSB, but have no defects in end-joining repair. Using mutants of downstream components of the checkpoint response, I also demonstrate that loss of the checkpoint function in DmATR mutants accounts for most, but not all of the defects reported. Furthermore, I analyzed the role of DmATR in response to endogenous damage that results from reducing Pola, a polymerase required for DNA synthesis. In the absence of DmATR, reductions in Pola result in developmental defects, P53-dependent cell death, and genome instability. This work implies that there is a function of DmATR that responds to endogenous damage that is independent of its checkpoint response. Both studies of DmATR suggest an intricate interaction of multiple DNA damage response pathways to ensure accurate repair, cell survival, proper development, and maintenance of genome stability. |
