Exposure of living organisms to environmental agents, such as ultraviolet sunlight, ionizing radiation and numerous chemicals, causes DNA damage. If not repaired, damaged DNA promotes the formation of mutations and cancer. Therefore, studies on the mechanisms by which damaged DNA is repaired are of primary importance. Since DNA repair in yeast presents all the hallmarks of DNA repair in human cells, it will be used in the proposed research as the model organism to study DNA repair. Clearly, increasing our understanding of the DNA repair mechanisms involved in maintaining the stability of the genome will help to define the role of DNA protection systems in cancer prevention.