The general objective is to understand the detailed processes involved in cellular repair of DNA and their effects on the radiation response of cells. This includes the photoenzymatic repair of ultraviolet damage (the simplest mechanism and the most amenable to analysis), and its interaction with the other types of cellular repairs. The methodology utilizes the light-dependence of photoenzymatic repair to unravel individual steps in the enzyme reaction. The project deals with cloning the gene for photoreactivating enzyme of E. Coli and amplification of the gene products, with photo repair and with dark-repair-deficient (UV-sensitive) mutants in mammalian cells.