In Escherichia coli, a common response to environmental stress is alteration in the pattern of gene expression. The transcriptional factor sigma S, encoded by the rpoS gene, is used by the cell to transcribe genes required to respond to a variety of environmental stresses. Production of sigma S in the cell is controlled translationally during osmotic stress. The non-coding RNA molecule DsrA binds to RpoS mRNA, promoting formation of a translationally active RpoS mRNA conformation that readily participates in translational initiation. This project investigates structural differences between translationally active and inactive RpoS mRNA structures using nuclease mapping. Kinetic studies will be performed to determine the mechanistic steps of DsrA mediated translational activation. This laboratory has recently shown that DsrA interacts specifically, and in a novel binding site, with the small subunit of the E. coli ribosome in vitro. Photo-induced chemical crosslinking of DsrA to the ribosomal subunit will be used to determine the specific amino acids and nucleotides of the ribosome and DsrA that interact. These studies will assist characterization of the novel RNA binding site on the ribosome. The project will provide general insight into the roles of non-coding RNAs in biology and in induction of the environmental stress response in E. coli. This work will directly integrate research with undergraduate education. The experimental plan is designed to allow undergraduate students to participate in all parts of this project, including data acquisition, experimental design, paper authorship and presentations at national research conferences.