4icg

Publication Abstract from PubMed

The bacterial nucleoid associated proteins Hha and H-NS jointly repress horizontally acquired genes in Salmonella, including essential virulence loci encoded within Salmonella pathogenicity islands. Hha is known to interact with the N-terminal dimerization domain of H-NS, however the manner in which this interaction enhances transcriptional silencing is not understood. To further understand this process we solved the X-ray crystal structure of Hha in complex with the N-terminal dimerization domain of H-NS (H-NS1-46) to 3.2 A resolution. Two monomers of Hha bind to symmetrical sites on either side of the H-NS1-46 dimer. Disruption of the Hha/H-NS interaction by the H-NS site-specific mutation I11A, results in increased expression of the Hha/H-NS co-regulated gene hilA without affecting the expression levels of proV, a target gene repressed by H-NS in an Hha-independent fashion. Examination of the structure revealed a cluster of conserved basic amino acids that protrude from the surface of Hha on the opposite side of the Hha/H-NS1-46 interface. Hha mutants with a diminished positively charged surface maintain the ability to interact with H-NS but can no longer regulate hilA. Increased expression of the hilA locus did not correspond to significant depletion of H-NS at the promoter region in chromatin immunoprecipitation assays. However in vitro, we find Hha improves H-NS binding to target DNA fragments. Taken together, our results show for the first time how Hha and H-NS interact to direct transcriptional repression and reveal that a positively charged surface of Hha enhances the silencing activity of H-NS nucleoprotein filaments.

Structural Insights into the Regulation of Foreign Genes in Salmonella by the Hha/H-NS Complex.,Ali SS, Whitney JC, Stevenson J, Robinson H, Howell PL, Navarre WW J Biol Chem. 2013 Mar 20. PMID:23515315^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.