H-NS cooperative binding to high-affinity sites in a regulatory element results in transcriptional silencing.
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.
Bouffartigues
Emeline
E
Laboratoire de Biotechnologie et Pharmacologie génétique Appliquée (LBPA), UMR 8113 CNRS, Ecole Normale Supérieure, 61 Avenue du Président Wilson, 94235 Cachan, France.
Buckle
Malcolm
M
Badaut
Cyril
C
Travers
Andrew
A
Rimsky
Sylvie
S
D001426:Bacterial Proteins / Q000378:metabolism*; D001665:Binding Sites; D004268:DNA-Binding Proteins / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D020868:Gene Silencing; D009154:Mutation / Q000502:physiology; D011485:Protein Binding; D050436:Regulatory Elements, Transcriptional; D014158:Transcription, Genetic
D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; C031908:H-NS protein, bacteria