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19The alternative sigma factor RpoS is an important regulatory protein in Escherichia coli, 20 responsible for mediating the general stress response. RpoS levels vary continuously in response 21 to different stresses. Previous work has shown that genes vary in their responsiveness to 22 increasing RpoS concentrations, with some genes being "sensitive," requiring only a low level of 23RpoS to be relatively highly expressed, while other genes are "insensitive," only being highly 24 expressed in the presence of high levels of RpoS. In other systems, this type of variation is 25 caused by interactions between the regulatory protein and the DNA it binds. To see if this is the 26 case for RpoS, we measured twelve RpoS binding site mutants for their effects on maximal 27 expression and responsiveness to increasing RpoS concentration. While maximal expression 28 varied over an order of magnitude across these twelve constructs, the responsiveness to 29 increasing RpoS concentration was largely unaffected, suggesting that the RpoS binding site 30 alone is not responsible for a genes' sensitivity or insensitivity to RpoS. In addition, we swapped 31 the RpoS binding region between sensitive and insensitive promoters and found no change in the 32 behavior of the promoter. Taken together, these results argue that differences in sensitivity of 33 the RpoS-dependent promoters are not due to interactions between RpoS and the various DNA 34 sites it binds. 35 36