The synthesis of the small, cytoplasmic protein UspA universal stress protein A) of Escherichia coli is induced as soon as the cell growth rate falls below the maximal growth rate supported by the medium, regardless of the condition inhibiting growth. The increase in UspA synthesis appears to be the result of induction of the monocistronic uspA gene. Induction of this gene during a heat-shock treatment is demonstrated to be the result of transcriptional activation of a sigma 70-dependent promoter which has previously been shown to be activated also during carbon starvation-induced growth arrest. Mutant cells lacking UspA grow at rates indistinguishable from the isogenic parent at different temperatures and in the presence of different growth inhibitors but are impaired in their ability to survive prolonged periods of complete growth inhibition caused by a variety of diverse stresses, including CdCl2, H2O2, DNP, CCCP exposure, and osmotic shock. Moreover, the uspA mutation results in an increased sensitivity of cells to carbon-source starvation (i.e. glucose, glycerol or succinate depletion). Also, the mutation causes a marked alteration in the timing of starvation protein expression but protein expression during steady- state growth appears to be normal. The results presented have prompted us to postulate that UspA may have a general protective function related to the growth arrest state.
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