RpoS-INDEPENDENT AND GROWTH PHASE-DEPENDENT EXPRESSION OF dcuSR OPERON OF ESCHERICHIA COLI

The dcuSR operon of Escherichia coli encodes a two-component sensor/kinase-response/regulator system. This system regulates gene expression in response to external C-4-dicarboxylates. During entry into stationary phase Gram-negative bacteria express genes that impart cellular resistance to environmental stresses. In E. coli, 50 or more genes are triggered by sigma factor (sigma(s)) during entry into stationary phase. Multi-copy dcuS-lacZ and chromosomally integrated dcuS-lacZ fusions analysis showed that the expression of dcuSR is positively regulated during growth phase. Many genes that are required for stationary-phase adaptation are controlled by RpoS, a conserved alternative sigma factor, whose expression is, in turn, controlled by many factors. To understand whether the dcuSR is dependent upon RpoS, a RpoS-dcuS-lacZ strain was generated. beta-Galactosidase assay and Western blot analysis reported that the generated RpoS-dcuS-lacZ strain and the wild type showed the same expression during stationary phase. Surprisingly, the growth phase-dependence of the expression of dcuSR is still present in RpoS-dcuS-lacZ strain suggesting that other growth-phase-dependent regulatory mechanisms (might be the DcuSR system or cAMP/CRP), in addition to RpoS, may control post-exponential dcuSR expression.