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Nat Struct Mol Biol. 2007 May;14(5):441-8. Epub 2007 Apr 15.

H-NS cooperative binding to high-affinity sites in a regulatory element results in transcriptional silencing.

Author information

1
Laboratoire de Biotechnologie et Pharmacologie génétique Appliquée (LBPA), UMR 8113 CNRS, Ecole Normale Supérieure, 61 Avenue du Président Wilson, 94235 Cachan, France.

Abstract

H-NS is a protein of the bacterial nucleoid involved in DNA compaction and transcription regulation. In vivo, H-NS selectively silences specific genes of the bacterial chromosome. However, many studies have concluded that H-NS binds sequence-independently to DNA, leaving the molecular basis for its selectivity unexplained. We show that the negative regulatory element (NRE) of the supercoiling-sensitive Escherichia coliproU gene contains two identical high-affinity binding sites for H-NS. Cooperative binding of H-NS is abrogated by changes in DNA superhelical density and temperature. We further demonstrate that the high-affinity sites nucleate cooperative binding and establish a nucleoprotein structure required for silencing. Mutations in these sites result in loss of repression by H-NS. In this model, silencing at proU, and by inference at other genes directly regulated by H-NS, is tightly controlled by the cooperativity between bound H-NS molecules.

PMID:
17435766
DOI:
10.1038/nsmb1233
[Indexed for MEDLINE]

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