EFFECTS OF SIGMA(S) AND THE TRANSCRIPTIONAL ACTIVATOR APPY ON INDUCTION OF THE ESCHERICHIA-COLI HYA AND CBDAB-APPA OPERONS IN RESPONSE TO CARBON AND PHOSPHATE STARVATION

The transcriptional regulation of two energy metabolism operons, hya a nd cbdAB-appA, has been investigated during carbon and phosphate starv ation. The hya operon encodes hydrogenase 1, and the cbdAB-appA operon encodes cytochrome bd-II oxidase and acid phosphatase, pH 2.5. Both o perons are targets for the transcriptional activator AppY. In exponent ial growth, expression of the hya and cbd operons was reduced in an rp oS mutant lacking the RNA polymerase sigma(S) factor, and the inductio n of the two operons by entry into stationary phase in rich medium was strongly dependent on sigma(S). Both operons were induced by carbon s tarvation, but only induction of the hya operon was dependent on sigma (S), whereas that of the cbd promoter was dependent on AppY. The appY gene also showed sigma(S)-dependent induction by carbon starvation. Th e cbd and hya operons were also found to exhibit a sigma(S)-dependent transient twofold induction by osmotic upshift. Like the cbd operon, t he hya operon was highly induced by phosphate starvation. For both ope rons the induction was strongly dependent on AppY. The induction ratio of the two operons was the same in rpoS(+) and rpoS mutant strains, i ndicating that the phosphate starvation-induced increase in sigma(S) c oncentration is not involved in the phosphate regulation of these oper ons.