Alternate SIyA and H-NS nucleoprotein complexes control hlyE expression in Escherichia coli K-12

• Published in: Molecular microbiology Vol. 66; no. 3; p. 685
• Main Authors: Lithgow, James K, Haider, Fouzia, Roberts, Ian S, Green, Jeffrey
• Format: Journal Article
• Language: English
• Published: Oxford Blackwell Publishing Ltd 01.11.2007
• Subjects: Biochemistry; E coli; Proteins; Ribonucleic acid; RNA; Salmonella; Toxins
• ISSN: 0950-382X; 1365-2958

Haemolysin E is a cytolytic pore-forming toxin found in several Escherichia coli and Salmonella enterica strains. Expression of hlyE is repressed by the global regulator H-NS (histone-like nucleoid structuring protein), but can be activated by the regulator SlyA. Expression of a chromosomal hlyE-lacZ fusion in an E. coli slyA mutant was reduced to 60% of the wild-type level confirming a positive role for SlyA. DNase I footprint analysis revealed the presence of two separate SlyA binding sites, one located upstream, the other downstream of the hlyE transcriptional start site. These sites overlap AT-rich H-NS binding sites. Footprint and gel shift data showed that whereas H-NS prevented binding of RNA polymerase (RNAP) at the hlyE promoter (PhlyE), SlyA allowed binding of RNAP, but inhibited binding of H-NS. Accordingly, in vitro transcription analyses showed that addition of SlyA protein relieved H-NS-mediated repression of hlyE. Based on these observations a model for SlyA/H-NS regulation of hlyE expression is proposed in which the relative concentrations of SlyA and H-NS govern the nature of the nucleoprotein complexes formed at PhlyE. When H-NS is dominant RNAP binding is inhibited and hlyE expression is silenced; when SlyA is dominant H-NS binding is inhibited allowing RNAP access to the promoter facilitating hlyE transcription. [PUBLICATION ABSTRACT]