Mutual regulation of Crl and Fur in Escherichia coli W3110

Abstract

The small regulatory protein Crl controls the expression of curli. Recently we have shown that Crl interacts directly with one of the most global regulators of Escherichia coli, the stress-related σ, factor RpoS, suggesting a more global role for Crl. We show here by a proteomics analysis that the expression of at least nine cellular proteins was considerably modified when Crl was overexpressed. We assessed the part of transcriptional and post-transcriptional regulation for five of these genes. The results showed that Crl regulates the expression of another global regulator, the central regulator of iron homeostasis, Fur. A molecular analysis revealed that Crl and Fur affect their own and each other's expression. We provide physical evidence for the binding of Fur to the crl and fur promoter regions. Crl modulated the affinity of Fur at the fur promoter but not at the crl promoter. The triad RpoS-Crl-Fur may thus represent the centerpiece of a global regulatory system of response to different stresses. © 2007 by The American Society for Biochemistry and Molecular Biology, Inc.