Date of Graduation


Document Type


Degree Type



School of Medicine


Microbiology, Immunology, and Cell Biology

Committee Chair

Tom Elliott.


RpoS is an alternative sigma factor which is required for the expression of genes that help bacteria cope with environmental stress. The regulation of RpoS is multifactorial and occurs at the levels of synthesis and protein turnover. Our lab has previously identified a rpoS translation enhancing factor in Salmonella typhimurium, the RNA-binding protein HF-I. An antisense element consisting of rpoS mRNA secondary structure is predicted to sequester the rpoS ribosome binding site and inhibit translation. HF-I may interact with this element to increase translation. Using rpoS genetic fusions, we have shown that native rpoS promoters can be substituted with tac or lacUV5 promoters without altering the normal HF-I mediated rpoS regulation. A long deletion from the 5 ' end of the rpoS transcript, which still contains the antisense element, was no longer regulated by HF-I. This suggests that HF-I may not simply interact with the secondary structure to enhance rpoS translation.;DsrA is a small untranslated RNA which has been shown to stimulate rpoS translation. We have shown that DsrA RNA interacts directly with rpoS mRNA. Mutational analysis has identified which RNA bases are important for the pairing between DsrA and rpoS mRNA that enhances rpoS translation.;The protein stability of RpoS is controlled by a putative two-component regulatory system. This system contains a protease, ClpXP, and a putative response regulator, MviA in S. typhimurium. We have tested several models which may explain MviA action and have confirmed that RpoS protein stability in S. typhimurium is dependent on the same genes as in Escherichia coli. We have shown that phosphorylation of MviA is important for its activity and that the source of this phosphate is probably not acetyl phosphate or the PTS system. Additionally, we observed an increase of RpoS during exponential growth on acetate as the sole carbon and energy source. Surprisingly, this RpoS increase during growth on acetate is independent of HF-I action.