THE SIGMA(S) LEVEL IN STARVING ESCHERICHIA-COLI-CELLS INCREASES SOLELY AS A RESULT OF ITS INCREASED STABILITY, DESPITE DECREASED SYNTHESIS

The sigma(S) level in starving (stationary phase) Escherichia coli cel ls increases four- to sixfold following growth in a defined or a compl ex medium. Chemostat-grown cells, subjected to increasing carbon starv ation, also become progressively richer in sigma(S) content. These inc reases occur despite reduced transcription of the sigma(S)-encoding ge ne, rpoS, and translation of rpoS mRNA, and result solely from a large increase in the stability of the sigma protein. Previous results, bas ed on rpoS ::lacZ transcriptional and translational fusions, and on me thionine incorporation in sigma(S), had suggested increased synthesis of sigma(S) in starving cells. Alternative explanations for these resu lts consistent with the conclusions of this paper are discussed.