Faithful replication of the genome is paramount for maintaining the fitness of an organism. Therefore, life has evolved inducible mechanisms to be able to repair damaged DNA and maintain evolutionary fitness. The SOS response is a highly conserved DNA damage inducible response that is tightly regulated. Multiple factors contribute to the ability of the cell to perform proper DNA repair and induction of the SOS response including the amount of RecA, mutations in RecA that affect competition for DNA, and other proteins that interact with the RecA filament. The complex relationship between RecA and LexA is the subject of this work. This dissertation is comprised of two projects examining the genetics of the SOS response. In the first chapter, we overexpress a noncleavable mutant of lexA, lexA3, and demonstrate an association between high expression of lexA3, severe ultraviolet light sensitivity, and an increased number of punctate RecA-GFP structures. While the explanation for this phenotype is not completely clear, we were able to show that a four- vi fold increase in lexA3 expression led to a nearly ten-fold decrease in recA expression. The second chapter examines the role of charge at position 38 and position 184 in RecA, that are the sites of the recA730 and recA1202 mutations, respectively. These mutations confer a phenotype whose hallmark is constitutive expression of the SOS response. Upon substituting different residues at positions 38 and 184, we were able to show that a positive charge at these positions is associated with constitutive SOS expression. Together, these studies show the complexity that surrounds the SOS response in E. coli