Role of Human and Mouse Rad54 in DNA Recombination and Repair

DNA double-strand breaks (DSBs) which can be induced by endogenously produced radicals or by ionizing radiation are among the most genotoxic DNA lesions. Repair of DSBs is of cardinal importance for the prevention of chromosomal fragmentation, translocations, and deletions. The genetic instability resulting from persistent or incorrectly repaired DSBs can eventually result in cancer. Therefore, to understand the biological consequences of exposure to ionizing radiation, insight into the mechanisms of DSB repair in mammalian cells is essential. The pace of identification of mammalian DSB repair genes has rapidly increased over the last few years. However, the functional analysis of the encoded proteins and the analysis of the role of the different DSB repair mechanisms in mammals are far from complete. This thesis describes the generation and phenotypic characterization of cells and mice, with a defect in one of the DSB repair genes, the RAD54 recombinational DNA repair gene. Furthermore, the initial characterization and cellular behavior of the mammalian Rad54 protein is described. Chapter 1 outlines the current knowledge on the role and molecular mechanisms of the multiple pathways that have evolved for the repair of DSBs. Our main findings concerning mammalian Rad54 at the protein and cellular level are discussed and integrated in the emerging picture of the DSB repair mechanisms in mammals. Chapters 2 and 3 describe the isolation of mammalian RAD54 genes and genomic characterization of the mouse RAD54 gene. Chapters 4 and 5 describe the generation and phenotypic characterization of RAD54 knockout cells and mice. Chapters 6 and 7 describe the characterization of the in vitro activities of the purified human Rad54 protein and the cellular behavior of the mouse Rad54 protein upon induction of DNA damage.