FIG. 1.

Various levels of σ^S regulation are differentially affected by various stress conditions. An increase of the cellular σ^S level can be obtained either by stimulating σ^S synthesis at the levels of rpoS transcription or rpoS mRNA translation or by inhibiting σ^S proteolysis (which under nonstress conditions is extraordinarily rapid). The most rapid and strongest reaction can be achieved by a combination of these processes (as observed, e.g., on hyperosmotic or pH shifts). For further details, see the text.