Differential effects and interactions of endogenous and horizontally acquired H‐NS‐like proteins in pathogenic Escherichia coli

Claudia M Müller,Bernt Eric Uhlin,Jörg Hacker,Ulrich Dobrindt,Levente Emödy,György Schneider

doi:10.1111/j.1365-2958.2009.06995.x

Abstract

The nucleoid-associated protein H-NS is important for gene regulation in Escherichia coli. We have studied H-NS interaction with StpA and an uncharacterized H-NS-like protein, Hfp, in the uropathogenic E. coli isolate 536 that expresses all three nucleoid-associated proteins. We found distinct interactions of the three proteins at the protein level, resulting in the formation of heteromers, as well as differences in their gene expression at the transcriptional level. Mutants lacking either StpA or Hfp alone did not exhibit a phenotype at 37°C, which is consistent with a low level of expression at that temperature. Expression of the hfp and stpA genes was found to be induced by apparently diametrical conditions, and StpA and Hfp levels could be correlated to modulatory effects on the expression of different H-NS targets, the bgl operon and operons for virulence factors such as fimbriae and capsular polysaccharide. The hns/hfp and hns/stpA double mutants displayed severe growth defects at low and high temperatures respectively. Our findings demonstrated different requirements for the alternative H-NS/Hfp/StpA combinations under these growth conditions. We propose that Hfp and StpA have distinct functions and roles in a dynamic pool of nucleoid-associated proteins that is adapting to requirements in a particular environment.

Highlights

The bacterial nucleoid is organized in a heterogeneous manner containing areas with highly condensed, quiescent DNA, and areas that are accessible for proteins involved in DNA processes such as replication, repair and transcription
The effects of H-NS have been studied in detail in non-pathogenic E. coli, where it first was suggested to cause transcriptional silencing and now is considered as a global regulator of gene expression (Göransson et al, 1990; Atlung and Ingmer, 1997; Hommais et al, 2001)
The genes coding for H-NS and StpA can be found in the chromosome of all characterized E. coli variants

Summary

Introduction

The bacterial nucleoid is organized in a heterogeneous manner containing areas with highly condensed, quiescent DNA, and areas that are accessible for proteins involved in DNA processes such as replication, repair and transcription. In Escherichia coli, several small proteins with DNA-binding activity play an important role in shaping the structure of the nucleoid and, simultaneously, in ensuring its flexibility. These so-called nucleoid-associated proteins affect the architecture of the nucleoid by either bending or bridging DNA (Dame, 2005; Luijsterburg et al, 2006).

Results

Discussion

Conclusion