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Increased Bending Rigidity of Single DNA Molecules by H-NS, a Temperature and Osmolarity Sensor

Department of Physics of Complex Systems, The Weizmann Institute of Science, Rehovot 76100, Israel; and ^* Department of Molecular Genetics and Biotechnology, The Hebrew University-Hadassah Medical School, Jerusalem 91010, Israel

Correspondence: Address reprint requests to Joel Stavans, Dept. of Physics of Complex Systems, The Weizmann Institute, Rehovot 76100, Israel. Tel.: 972-8-9342615; Fax: 972-8-9344109; E-mail: joel.stavans{at}weizmann.ac.il.

Histonelike nucleoid structuring protein (H-NS) is an abundant prokaryotic protein participating in nucleoid structure, gene regulation, and silencing. It plays a key role in cell response to changes in temperature and osmolarity. Force-extension measurements of single, twist-relaxed -DNA-H-NS complexes show that these adopt more extended configurations compared to the naked DNA substrates. Crosslinking indicates that H-NS can decorate DNA molecules at one H-NS dimer per 15–20 bp. These results suggest that H-NS polymerizes along DNA, forming a complex of higher bending rigidity. These effects are not observed above 32°C or at high osmolarity, supporting the hypothesis that a direct H-NS-DNA interaction plays a key role in gene silencing. Thus, we propose that H-NS plays a unique structural role, different from that of HU and IHF, and functions as one of the environmental sensors of the cell.

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