Question: Shigella flexneri is an intracellular pathogen closely related to E. coli and S. typhimurium. Some experiments have shown that oxygen controls expression of some virulence factors in this organism. Assume that you have a S. flexneri gene, oxyA, that appears to code for a virulence factor and is only expressed in the absence of oxygen. Design a set of experiments to: 1) identify additional genes that are also expressed in the absence of oxygen but not in the presence of oxygen and 2) determine if expression of the oxyA gene in the absence of oxygen is due to the action of a repressor or an activator protein. Be sure to describe any strains or clones you would need to create to carry out your experiments and the kind of results you would expect from each experiment.