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Originally published In Press as doi:10.1074/jbc.M211766200 on March 13, 2003
J. Biol. Chem., Vol. 278, Issue 21, 18754-18760, May 23, 2003
A Novel H-NS-like Protein from an Antarctic Psychrophilic Bacterium Reveals a Crucial Role for the N-terminal Domain in Thermal Stability*
Christian Tendeng ,
Evelyne Krin ,
Olga A. Soutourina ¶,
Antoine Marin ||,
Antoine Danchin ** and
Philippe N. Bertin  
From the
Unité de Génétique des Génomes Bactériens, Institut Pasteur, 75724 Paris Cedex 15, France,
¶ Laboratoire de Biochimie, Ecole Polytechnique, 91128 Palaiseau Cedex, France,
|| Atelier de Bio-informatique, Université Paris 6, 12 rue Cuvier, 75005 Paris, France,
** HKU-Pasteur Research Centre, Dexter HC Man Building, 8 Sassoon Road, Pokfulam, Hong Kong, China,
 Laboratoire de Dynamique, Evolution et Expression de Génomes de Microorganismes, FRE 2326, Université Louis Pasteur/CNRS, 67083 Strasbourg Cedex, France
We describe here new members of the H-NS protein family identified in a psychrotrophic Acinetobacter spp. bacterium collected in Siberia and in a psychrophilic Psychrobacter spp. bacterium collected in Antarctica. Both are phylogenetically closely related to the HvrA and SPB Rhodobacter transcriptional regulators. Their amino acid sequence shares 40% identity, and their predicted secondary structure displays a structural and functional organization in two modules similar to that of H-NS in Escherichia coli. Remarkably, the Acinetobacter protein fully restores to the wild-type H-NS-dependent phenotypes, whereas the Psychrobacter protein is no longer able to reverse the effects of H-NS deficiency in an E. coli mutant strain above 30 °C. Moreover, in vitro experiments demonstrate that the ability of the Psychrobacter H-NS protein to bind curved DNA and to form dimers is altered at 37 °C. The construction of hybrid proteins containing the N- or the C-terminal part of E. coli H-NS fused to the C- or N-terminal part of the Psychrobacter protein demonstrates the role of the N-terminal domain in this process. Finally, circular dichroism analysis of purified H-NS proteins suggests that, as compared with the E. coli and Acinetobacter proteins, the -helical domain displays weaker intermolecular interactions in the Psychrobacter protein, which may account for the low thermal stability observed at 37 °C.
Received for publication, November 19, 2002
, and in revised form, February 24, 2003.
 To whom correspondence should be addressed: Laboratoire de Dynamique, Evolution et Expression de Génomes de Microorganismes, Université Louis Pasteur, 28 rue Goethe, 67000 Strasbourg, France. Tel.: 33-3-19-24-20-08; Fax: 33-3-19-24-20-28; E-mail: bertin{at}gem.u-strasbg.fr.

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Copyright © 2003 by the American Society for Biochemistry and Molecular Biology.
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