dps expression in Escherichia coli O157 : H7 requires an extended - 10 region and is affected by the cAMP receptor protein

The DNA binding protein from starved cells (Dps) is a general stress protein that provides Escherichia coli protection from osmotic, oxidative, and acid stresses. While Dps production and accumulation is primarily associated with stationary phase, during log phase, this protein protects against oxidative stress in an OxyR-dependent manner. In this study, evidence is provided that expands the role of Dps in acid tolerance to both log- and stationary-phase E. coli O157:H7. The transcription of aps occurred in log-phase cells without OxyR or stress and was upregulated during entry into stationary phase. The expression in log and stationary phase involved sigma(70) and sigma(s), respectively, with both sigma factors recognizing the same promoter region. Site-directed mutagenesis identified an extended -10 region that was essential to both sigma(70) and sigma(s) transcription of dps. cAMP receptor protein (CRP) was found to repress aps expression as a crp mutant had a significant increase in the aps mRNA level. However, a CRP binding site was not found in the aps promoter and upregulation of dps in the crp mutant was absent in a crp rpoS double mutant. The findings from this study demonstrated that dps was expressed at a basal level during growth, both sigma(70) and sigma(s)-driven transcription required an extended -10. and CRP repression is mediated through the alternative sigma factor sigma(s) (rpoS). (c) 2006 Elsevier B.V. All rights reserved.