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by Keyword: Transcription repression


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de Alba, C. F., Solorzano, C., Paytubi, S., Madrid, C., Juarez, A., Garcia, J., Pons, M., (2011). Essential residues in the H-NS binding site of Hha, a co-regulator of horizontally acquired genes in Enterobacteria FEBS Letters , 585, (12), 1765-1770

Proteins of the Hha/YmoA family co-regulate with H-NS the expression of horizontally acquired genes in Enterobacteria. Systematic mutations of conserved acidic residues in Hha have allowed the identification of D48 as an essential residue for H-NS binding and the involvement of E25. Mutations of these residues resulted in deregulation of sensitive genes in vivo. D48 is only partially solvent accessible, yet it defines the functional binding interface between Hha and H-NS confirming that Hha has to undergo a conformational change to bind H-NS. Exposed acidic residues, such as E25, may electrostatically facilitate and direct the approach of Hha to the positively charged region of H-NS enabling the formation of the final complex when D48 becomes accessible by a conformational change of Hha. Structured summary of protein interactions: YdgT and H-NS bind by nuclear magnetic resonance (View interaction) Hha and H-NS bind by nuclear magnetic resonance (View Interaction 1, 2, 3) Hha physically interacts with H-NS by pull down (View Interaction 1, 2).

Keywords: Nucleoid associated protein, H-NS, Hha, Transcription repression


Garcia, J., Madrid, C., Cendra, M., Juarez, A., Pons, M., (2009). N9L and L9N mutations toggle Hha binding and hemolysin regulation by Escherichia coli and Vibrio cholerae H-NS FEBS Letters , 583, (17), 2911-2916

Proteins of the Hha/YmoA family co-regulate with H-NS the expression of virulence factors in Enterobacteriaceae. Vibrio cholerae lacks Hha-like proteins and its H-NS (vcH-NS) is unable to bind Hha, in spite of the conservation of a key residue for Hha binding by Escherichia coli H-NS (ecH-NS). Exchange of the residues in position 9 between vcH-NS and ecH-NS strongly reduces Hha binding by ecH-NS and introduces it in vcH- NS. These mutations strongly affect the repression of the hemolysin operon in E. coli and the electrophoretic mobility of complexes formed with a DNA fragment containing its regulatory region.

Keywords: Nucleoid associated protein, H-NS, Hha, Transcription repression, NMR, Electrophoretic mobility shift assays


Cordeiro, Tiago N., García, Jesús, Pons, José-Ignacio, Aznar, Sonia, Juárez, Antonio, Pons, Miquel, (2008). A single residue mutation in Hha preserving structure and binding to H-NS results in loss of H-NS mediated gene repression properties FEBS Letters , 582, (20), 3139-3144

In this study, we report that a single mutation of cysteine 18 to isoleucine (C18I) in Escherichia coli Hha abolishes the repression of the hemolysin operon observed in the wild-type protein. The phenotype also includes a significant decrease in the growth rate of E. coli cells at low ionic strength. Other substitutions at this position (C18A, C18S) have no observable effects in E. coli growth or hemolysin repression. All mutants are stable and well folded and bind H-NS in vitro with similar affinities suggesting that Cys 18 is not directly involved in H-NS binding but this position is essential for the activity of the H-NS/Hha heterocomplexes in the regulation of gene expression.

Keywords: Nucleoid-associated protein, H-NS, Hha, Transcription repression