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J. Bacteriol., Aug 1996, 4335-4343, Vol 178, No. 15
Copyright © 1996, American Society for Microbiology

Probing the structure, function, and interactions of the Escherichia coli H-NS and StpA proteins by using dominant negative derivatives

RM Williams, S Rimsky and H Buc
Unite de Physicochimie des Macromolecules Biologiques (URA 1149 du Centre National de la Recherche Scientifique), Institut Pasteur, Paris, France.

Twelve different dominant negative mutants of the Escherichia coli nucleoid-associated protein, H-NS, have been selected and characterized in vivo. The mutants are all severely defective in promoter repression activity in a strain lacking H-NS, and they all disrupt the repression normally exerted by H-NS at two of its target promoters. From the locations of the alterations in these mutants, which result in both large truncations and amino acid substitutions, we propose that H-NAS contains at least two distinct domains. The in vitro protein-protein cross-linking data presented in this report indicate that the proposed N-terminal domain of H-NS has a role in H-NS multimerization. StpA is a protein with known structural and functional homologies to H-NS. We have analyzed the extent of these homologies by constructing and studying StpA mutants predicted to be dominant negative. Our data indicate that the substitutions and deletions found in dominant negative H-NS have similar effects in the context of StpA. We conclude that the domain organizations and functions in StpA and H-NS are closely related. Furthermore, dominant negative H-NS can disrupt the activity of native StpA, and reciprocally, dominant negative StpA can disrupt the activity of native H-NS. We demonstrate that the N-terminal domain of H-NS can be chemically cross-linked to both full-length H-NS and StpA. We account for these observations by proposing that H-NS and StpA have the ability to form hybrid species.


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