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Requirement for the molecular adapter function of StpA at the Escherichia coli bgl promoter depends upon the level of truncated H‐NS protein
Author(s) -
Free Andrew,
Porter Megan E.,
Deighan Padraig,
Dorman Charles J.
Publication year - 2001
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1046/j.1365-2958.2001.02678.x
Subject(s) - biology , gene silencing , rpos , operon , tn10 , escherichia coli , genetics , nucleoid , repressor , dna binding protein , psychological repression , transcription factor , transcription (linguistics) , dna , microbiology and biotechnology , promoter , gene , enterobacteriaceae , gene expression , linguistics , philosophy
Truncated derivatives of the Escherichia coli nucleoid‐associated protein H‐NS that lack the DNA‐binding domain remain competent for silencing of the cryptic bgl operon in vivo . Previous studies have provided evidence for the involvement of either the homologous nucleoid protein StpA or the alternative sigma factor RpoS in this unusual silencing mechanism. Here, we rationalize this apparent discrepancy. We show that two hns alleles ( hns‐205 ::Tn 10 and hns60 ), which produce virtually identical amino‐terminal fragments of H‐NS, have very different requirements for StpA to mediate bgl silencing. The hns60 allele produces a high level of truncated H‐NS, which can overcome the absence of StpA, whereas the lower level expressed by hns‐205 ::Tn 10 requires StpA for silencing. Reversing the relative levels of the two H‐NS fragments reverses their requirement for StpA to silence bgl transcription. This suggests that the amino‐terminal fragment of H‐NS can be targeted to DNA to mediate silencing by multiple protein–protein interactions. The high‐specificity interaction with StpA can function at low levels of truncated H‐NS, whereas an alternative mechanism, perhaps involving lower specificity interactions with another protein(s), is only functional when truncated H‐NS is abundant. These findings have important implications for the involvement of other proteins in H‐NS‐dependent transcriptional repression.