3. Characterization of the small RNA expressed by L. pneumophila. Recent studies have identified 79 sRNAs expressed by L. pneumophila. Two of these sRNAs, called RsmY and RsmZ, functionally link three major response regulators of L. pneumophila virulence factors, the sigma factor RpoS, the RNA-binding protein CsrA and the two-component system LetA/S. Another identified sRNA is a homolog of the 6S RNA of E. coli, which affects the balance between different RNAP holoenzymes. It is an important regulator of L. pneumophila virulence since a 6S RNA deletion mutant is unable to compete against the wild-type during intracellular growth. There is currently no insight into the role of the other identified sRNAs. Therefore, the goal of this project is to identify phenotypes controlled by the sRNAs expressed by L. pneumophila and to identify the targets of the sRNAs associated with a phenotype.