The natural environments of many bacteria often contain limiting amounts of nutrients and, therefore, sustain only sporadic growth. As a consequence Escherichia coli is well adapted to survival under feast-and-famine conditions. Unfortunately, our knowledge, based on studies of rapidly growing laboratory cultures, is heavily biased toward the feast lifestyle. The physiological and molecular changes that occur during the transition to famine have only recently gained attention. In E. coli the limitation of a nutrient below a certain level induces a response specific for that class of nutrient. The regulatory systems involved (cAMP/CRP for carbon sources, NtrBINtrCW for nitrogen, or PhoFUPhoB for phosphorus) control large groups of structural genes, whose gene products allow higher affinity uptake and metabolism of the class of nutrient. If sources are present in the growth medium, the cells continue to grow and divide. However, if the medium is totally exhausted for an essential nutrient, the cells enter stationary phase. This stationary phase response is clearly different from the nutrientspecific responses mentioned above, but it is similar no matter which medium is used to grow the cells. The stationary phase response involves drastic changes in cellular physiology and morphology: structural changes in the cell envelope, an altered membrane composition, and differences in DNA supercoiling and compactness (reviewed in Siegele and Kolter, 1992). Depending on medium composition, stationary phase cells synthesize storage compounds, such as glycogen and polyphosphates (Preiss, 1969) and protective substances, such as trehalose (Hengge-Aroniset al., 1991). Instationary phasecells, the RNA polymerase core is modified (Ozaki et al., 1991) and 100s dimers of 70s ribosome monomers occur (Wada et al., 1990). The synthesis of a set of stationary phase or postexponential proteins is induced, regardless of the class of nutrient for which the cells are starved (Groat et al., 1988).

A role in stress protection has been proposed for these proteins (Matin, 1991) since stationary phase cells are extremely resistant to heat shock (> 50%) and high concentrations of H202 and NaCl (Jenkins et al., 1988; Jenkins et al., 1990). The ability to survive under these very diverse stress conditions indicates that stationary phase cells possess systems not expressed in exponentially growing cells for DNA repair and the protection of membranes and proteins. The stimulus for induction of these systems cannot be the specific stress conditions, because multiple stress resistance is found in stationary phase cells that have never encountered a particular stress agent. This is in contrast with the induction of specific stress responses,