Starvation is a common experience of bacteria in most natural environments, including the hosts of pathogens, and such bacteria have applied importance. We have found that the nondifferentiating bacterium Escherichia coli selectively expresses several temporal classes of unique proteins in the first 3-5 hours of carbon starvation. This phenomenon generates stress-resistant cells (starvation, heat, oxidative and osmotic stresses). Three classes of such genes so far identified are: the cst genes--induced only under carbon starvation and requiring cyclic AMP/CRP; the csi genes--also induced by carbon starvation alone but independent of cAMp; and the pex genes--cAMP/CRP-independent and also induced by starvation for nutrients other than carbon. The genes of the latter classes appear responsible for the development of stress resistance, but the induction of all classes may depend on transcriptional systems unique to the postexponential phase. To explore this transcriptional system, we will clone and sequence one each of cst and csi genes, and two pex genes. For cloning the promoter and promoter-proximal regions of the nonessential genes, chromosomal (bla)lacZ fusions and defective plasmid-encoded bla gene reconstitution will be used; hybridization probes derived therefrom will be used in cloning the structural genes. For the essential genes alternate approaches, such as microsequencing of proteins isolated from 2-D PAGE, will be used. Using the cloned genes, the starvation gene dosage effect on survival will be investigated. Appropriate fusions will also be used to identify cis and trans acting regulatory components of the carbon starvation regulon.
