The purpose of the proposed research project is to elucidate the regulatory mechanisms that control coordinated induction of a group of adaptive functions (SOS functions) that are repressed in undamaged cells but are activated in response to DNA damage or interruption of DNA replication. SOS functions include: an error-prone DNA repair activity; prophage induction; transient inhibition of cell division; inhibition of DNA degradation, and others. Coordinated induction of SOS functions requires the recA ion lexA ion genotype and new protein synthesis after exposure to an SOS-inducing agent (ultraviolet (UV) light, nalidixic acid, thymine starvation, etc.). The regulation of SOS functions is complex, and involves the participation of many genes other than recA and lexA. We have observed that Sfi mutations (suppressors of filamentous growth) have pleiotropic effects on expression of SOS functions, on proteolytic activity and on outer membrane protein composition, as visualized by SDS-polyacrylamide gel electrophoresis. We propose to examine systematically the effects of individual Sfi mutations, and of controlled combinations of two or more, on SOS expression, proteolytic activity (i.e., the rate of degradation of various abnormal proteins) and the pattern of outer membrane proteins on gels. We propose also to isolate mutants lacking one or more major or minor outer membrane proteins, and to determine how this loss affects SOS expression and proteolytic activity. We intend also to determine how lambda prophage is induced by UV radiation in a lexA-strain in which synthesis of protein X (recA product) is not UV-inducible. We plan to define the genetic and molecular basis for the constitutive expression of SOS functions in a lexA plus strain, using gene amplification and heteroduplex analysis, as well as restriction mapping and conventional genetic mapping. We propose also to determine how altered subunits of DNA gyrase (caused by nalA and cou mutations) affect SOS regulation. Our goal is to achieve a comprehensive model to account for the coordinated repression of SOS functions in intact cells and for their coordinated induction in response to DNA-damaging treatments.