Under nonstress conditions, Rpos levels in the cell are low since rpos mRNA (messenger RNA) forms a stable secondary structure, which results in poor translation under normal conditions. RpoS protein (the actual sigma factor) is also repeatedlyde graded under normal nonstress conditions by the ClpXP protease in E. coli (Schweder and others 1996). As a result of these tran- scriptional and translation-level regulatory mechanisms in E. coli, the intracellular levels of as in growing nonstressed cells are lower than that of 0 (Jishage and others 1996). as is induced in response to into the stationary phase and also induced by stresses such as weak arvation, high osmolarity, and high low and so on. (Lange and 1994)