The object is to understand the effects of ultraviolet radiation (UV) on cellular processes, the repair of damages caused by the radiation, and the mutational consequences on the repair processes. A recently discovered effect of UV is the suppression of polarity, which is a premature termination of transciption. A theory will be tested that the UV depletes the activity of the transcription termination factor rho. Polarity will be studied in two genetic systems, the genes of bacteriophages phi X174 and G4, and the genes of the gal operon. The aims are to explain the function of the rho protein in the repair of cell damage and how UV prevents transcription termination. UV can also cause termination of transcription and that property will be used to provide a functional test for promoters. The aims are to determine if the use of distant promoters rather than proximal ones in a general strategy of viruses and to determine what signals are involved in specifying the translatable part of a messenger RNA. UV induces a repair process that is highly mutagenic. A mechanism has been proposed to explain the mutagenic effect and the theory will be tested by direct determination of the base changes produced by the mutations, and that will be done by DNA sequencing.