PROJECT SUMMARY The ability of bacteria to rapidly sense and respond to changes in the environment is fundamental to colonization and survival. Post-transcriptional regulation is emerging as an important strategy that promotes efficient and precise control of bacterial virulence, and thus plays a central role in pathogenesis. Enterohemorrhagic Escherichia coli O157:H7 (EHEC) is a bacterial pathogen that colonizes the human colon and causes severe hemorrhagic colitis and hemolytic uremic syndrome (HUS), which can be fatal. EHEC encodes several important virulence factors, including the potent Shiga toxin that causes HUS and a type three secretion system (T3SS) and effectors necessary for attaching and effacing (AE) lesion formation on enterocytes. EHEC has a very low infectious dose, suggesting that EHEC has evolved mechanisms to spatiotemporally control virulence gene expression to occur within appropriate host niches. RNA helicases are ubiquitous in all kingdoms of life, as well as within viral genomes, and are involved in virtually all aspects of RNA metabolism, including RNA degradation or protection and translation. Our studies underlie the importance of RNA helicases to EHEC niche adaptation and coordination of virulence gene expression. The proposed work will investigate the importance of RNA helicases to niche recognition and host-pathogen interactions using a physiologically relevant infection model. We will also utilize unbiased approaches to comprehensively map the regulon of an EHEC helicase and identify targets of regulation.