Department of Microbiology & Immunology Seminar
Speaker: Dr. Nadim Majdalani
Staff Scientist, Laboratory of Molecular Biology, Center for Cancer Research, NCI, Bethesda, MD
Title: “Polyamines are Needed for E. coli to Mount a General Stress Response”
Escherichia coli and related bacteria respond and adapt to environmental stresses via the specialized sigma factor RpoS that mediates the general stress response. RpoS-dependent activation of multiple genes allows cells to survive stationary phases and many different stresses and plays a role in the adaptation of bacteria to mammalian hosts. RpoS levels are regulated at multiple levels. Multiple small RNAs (sRNAs) positively regulate translation; degradation of RpoS, rapid during exponential growth, ceases upon starvation for many nutrients, significantly contributing to the accumulation of RpoS. An E. coli derivative unable to synthesize polyamines was found to have very low levels of RpoS. We find that this is primarily due to co-translational degradation of RpoS, possibly enhanced by pausing during translation. Changes in rpoS codon usage to optimize translation partially overcomes the defect in RpoS levels. Interestingly, wild-type strains carrying ribosomal mutation with more stringent proof-reading ribosomes also show a defect in RpoS accumulation due to rapid degradation and overcome by codon optimization. We suggest that rpoS is tuned, by codon usage, to be sensitive to slowed or stressed translation. This allows the co-translational degradation of RpoS, providing a new level of regulation of this Sigma factor.