It also regulates transcription of many other genes that participate in a variety of cellular functions, including genes involved in the following processes or responses: biogenesis of flagella |CITS: [8071234][10601207][11872702]|, transcription control of the type I fimbria structural genes |CITS: [9922259][9352908][9595659][7510658][9749677]|, acid resistance |CITS: [16204188]|, the functional glutamic acid-dependent system |CITS: [10383761]|, osmotically inducible genes |CITS: [9663683]|, the glutamate decarboxylase-dependent acid resistance system |CITS: [15795232][12446650][11976288][11298273]|, osmotic control |CITS: [8120010][11673423]|, the type II secretion pathway |CITS: [11118204]|, carbon sources |CITS: [2160266]|, genes involved in the RNA component of the small subunit (30S subunit) |CITS: [9632265][15686546]|, and proteases |CITS: [16143461]|, among others. It has also been shown to be involved in survival during stationary phase, conferring to the bacteria a growth advantage during stationary phase (GASP) |CITS: [22843842]|. A lack of H-NS results in overexpression of ycdT, ydeH, yeal, yeaJ, yaiC, csgD, iraP, and ydiV, while expression of fliA is decreased. These results indicate that H-NS influences motility via multiple regulatory linkages that include, minimally, the messenger molecule cyclic di-GMP, the biofilm regulatory protein CsgD, and the sigma factors σ^S and σ^F, thus impacting motility through diverse regulatory pathways |CITS: [26195595]|. H-NS is capable of inducing severe bends in the DNA, interacting with a large number of DNA regions that contain a planar curvature |CITS: [2126011][1745240][14627810]|. It has been suggested that H-NS binds strongly to sites carrying a 10-bp AT-rich consensus sequence, which functions as a nucleation site for the formation of a repressive higher-order nucleoprotein complex |CITS: [17881364][19740756]|. That AT-rich sequence for H-NS DNA binding is preferred for insertion of horizontally acquired genes, and H-NS appears to regulate the inserted genes |CITS: [31960057]|. H-NS binds to intergenic regions as well as regions within genes, but not all genes that bind H-NS are affected by this protein, a fact that is in agreement with the primary role assigned to HN-S in maintenance of nucleoid structure.There is a higher diversity in the sequence of HNS-bound intergenic regions than in HNS-unbound intergenic regions, and that diversity sometimes alters gene expression |CITS:[26789284]|. The HNS-bound regions have been conserved through evolution in the E. coli lineage|CITS:[26789284]|. Currently, there are different models for the formation of DNA-H-NS-DNA bridges which show that this protein binds in tandem to sequences in the genome, forming multimers |CITS: [15853876][17191074][16879983]|. H-NS both changes DNA rigidity and forms bridges between DNA molecules in the presence of Mg²⁺ |CITS:[29127381]|. The intrinsic curvature and flexibility of binding sites of H-NS were investigated. The preference of H-NS for high intrinsic curvature is not as clear as with other DNA-binding proteins. The binding sites for H-NS show no preference to specific curvature level, and the binding affinity for H-NS does not seem to depend on the level of intrinsic curvature |CITS:[29625128]|. The binding of H-NS along the DNA negatively correlates with transcriptional propensity and positively correlates with integration of foreign DNA and high AT content |CITS: [30904377]|. The main effect of H-NS on low transcription appears to be on the chromosomal integration region instead of an effect on specific promoters to which it binds |CITS: [30904377]|. Based on studies of single-molecule tracking, it was determined that on average, at any time 73% of H-NS molecules are in long-lived DNA-bound complexes at target sites, 27% are transiently, nonspecifically DNA-bound, and only 0.1% are in free diffusion between DNA strands; a diffusion coefficient of 0.41 μm²s^-1 was calculated |CITS: [33621478]|. As expected for a gene involved in the modulation of many cellular processes, the expression of hns is regulated by several systems and at different levels. At the transcription level, hns is autoregulated, and it is controlled by different transcription factors. hns is induced by high hydrostatic pressure |CITS: [8226663]| and DNA synthesis |CITS: [8596450]|. At the posttranscriptional level, it is subject to regulation by the sRNAs Hfq and DsrA |CITS: [11115103][12554874][15814430][15147838][12753181]|. It is a DNA-binding protein with similarity to StpA |CITS: [7961433][1480493]| and these two proteins can have similar functions |CITS: [10515926][10947847]|. It has an approximately fivefold-lower affinity for DNA than StpA and has a major preference for curved DNA |CITS: [11278075]|. StpA appears to be a backup for Hns in the regulation of a set of nonessential and recently acquired genes |CITS: [23661089]|. Expression of stpA from a plasmid can complement an hns mutant phenotype and StpA is able to repress and activate a subset of H-NS-regulated genes, but the specific mechanisms remain to be determined |CITS: [7961433][11278075][8890170][8635467][19151137][8890170]|. H-NS has two dimerization domains (N-terminal and central) and a C-terminal DNA-binding domain. The H-NS polypeptide can assemble as long polymeric filaments on DNA, and mutations in any of the three domains confer a dominant-negative phenotype in vivo by a subunit-poisoning mechanism |CITS:[30724731]|. A dominant negative form of StpA can disrupt H-NS activity and vice versa, and H-NS can interact with StpA at two distinct domains to form heterodimers in vitro; also, there is evidence that these proteins can form homodimers |CITS: [11244076][8755860][10203842][8755860]|. For this reason, in the absence of H-NS the StpA protein is rapidly degraded in a Lon protease-dependent manner |CITS: [11244076][10485902]|; protection from proteolytic degradation appears to be mediated by a direct interaction between StpA and H-NS |CITS: [11244076]|. On the other hand H-NS also may form heterotrimeric complexes with Hha and YdgT |CITS: [17116239][15458420]|. It was proposed that Hha enhances the oligomerization of Hns/StpA which is necessary to form DNA-protein filaments to repress transcription |CITS: [23543115][23601147]|. The high-resolution structure based on solid-state NMR spectra from full-length H-NS has been determined |CITS: [23601147]|. H-NS variants L26PHis, I119THis, and D93His are dominant-negative in vitro |CITS:[30724731]|. Another dominant-negative truncation mutant, D64 (which possesses only the proteins N-terminal domain)per se, completely and unexpectedly inhibited transcription in assay formats (initiation plus elongation, or elongation alone) |CITS:[30724731]|. It is proposed that under certain growth conditions, RNA polymerase is the direct inhibitory target of Hha, whose effect is mimicked by the isolated N-terminal domain of H-NS |CITS:[30724731]|. StpA and Hha stimulate pausing by RNA polymerase at 20^oC by promoting DNA-DNA bridging of H-NS filaments, through H-NS-mediated gene regulation |CITS:[29718386]|. Growth phase-dependent relocalization is shown by H-NS in response to hyperosmotic shock. A novel observation of a dynamic compaction of the bacterial chromosome in response to exposure to high levels of salt was reported |CITS:[31481544]|. It has been demonstrated that cAMP, GDP, GTP, and ppGGpp bind to H-NS, suggesting a modulatory effect of these nucleotides on the protein; nevertheless, no effect on gene expression in vitro was observed when ppGpp was bound to H-NS |CITS: [34360641]|. H-NS is a small protein and it is an abundant nucleic acid protein in the genome, with about 20,000 copies per cell. This regulator belongs to the histone-like family of transcriptional regulators, and the structure of the protein consists of two structured domains which are separated by a flexible linker |CITS: [15100692]|. The linker region connecting the N-terminal oligomerization and C-terminal DNA-binding domains promotes H-NS/DNA binding and thus plays an important role in H-NS gene silencing. H-NS does not play a major role in chromosomal compaction |CITS:[29109287]|. The N-terminal domain is required for oligomerization and it is involved in protein-protein interactions, while the purified C-terminal domain is involved in DNA binding |CITS: [15100692][10203842][8755860][15063845][19740756]|. The cooperative binding of H-NS to DNA is related to protein-protein interactions |CITS: [24275506]|. The N-terminal domain is composed of two dimerization sites, dimerization site-1 and site-2, which are both required for H-NS oligomerization. The dimerization site-2 of H-NS is required for gene silencing and nucleoprotein filament formation |CITS:[29695505]|. The concentration of H-NS is an important influence on the formation of H-NS-DNA assemblies. H-NS oligomerization is not sufficient in forming large structures of H-NS-DNA assemblies, indicating oligomerization along bacterial DNA is crucial |CITS:[31491518]|. There is compelling evidence against a parallel-to-antiparallel switch mechanism at site-1 and evidence of an autoinhibitory mechanism for heat-induced unfolding of site-2, which in turn allows interactions between the N-terminal and C-terminal domains of H-NS. Temperature provokes unfolding of the central dimerization domain, breaking up H-NS multimers. This unfolding event enables an autoinhibitory compact H-NS conformation that blocks DNA binding |CITS:[30597093]|. H-NS forms two compact clusters associated with each copy of the chromosome. These clusters are located near the one-quarter and three-quarter positions along the long axis of the cell |CITS: [21903814]|. In cells with three clusters, the additional cluster tends to appear in the middle |CITS: [21903814]|. The two cluster formations are induced by the N-terminal domain-driven oligomerization of the protein |CITS: [21903814]|. H-NS sequesters the regulated genes and operons into these clusters and juxtaposed numerous DNA segments broadly distributed throughout the chromosome |CITS: [21903814]|. Wang et al. (2011) reported that H-NS clusters could thus serve as anchoring points for numerous DNA loci distributed throughout the genome, creating DNA loops connecting the anchored loci |CITS: [21903814]|. Cellular treatment with silver nanoparticles (AgNPs) or Ag⁺ ions causes the formation of denser and larger clusters of H-NS at the center of the cell |CITS: [31212266]|. Ag⁺ ions led to faster diffusive dynamics of H-NS proteins |CITS:[31953329]|. Based on an electrophoretic mobility shift assay (EMSA) on purified H-NS protein and isothermal titration calorimetry, it was confirmed that Ag⁺ ions weaken the binding between H-NS proteins and DNA and that DNA and Ag⁺ ions interact directly |CITS:[31953329]|. It was found that the promoter islands, which are regions of DNA containing multiple transcription start sites, are recognized and inactivated by HNS. These promoter islands are associated with genes acquired horizontally |CITS: [23717391]|. Based on ChIP-chip and chip-seq analysis, it was proved that Rho-dependent termination abrogates the H-NS-DNA interactions, leading to transcriptional derepression of H-NS-silenced genes |CITS: [24499790]|. An hns-stpA double mutant displayed slow growth and resulted in high expression of otherwise-silent horizontally acquired genes |CITS: [25429971]|. H-NS engineered mutants showed enhanced acid tolerance |CITS:[30053876]|. Several mutations in the σ³⁸ (RpoS) factor, as well as a duplication of ~40% of the genome centered around the origin of replication, converge in partially redressing the transcriptional imbalance of a strain lacking the H-NS/StpA gene-silencing system. This findings suggests a possible role for σ³⁸ in transcription of many H-NS targets |CITS: [25429971]|. Transcription from a neighboring region extends into an H-NS-bound locus and it can disrupt local H-NS repression in a dose-dependent manner, indicating a novel mechanism by which H-NS-mediated silencing can be reversed |CITS: [29424946]|. Rangarajan and Schnetz showed that when transcription from a neighboring region extends into an H-NS-bound locus, it can disrupt local H-NS repression in a dose-dependent manner, indicating a novel mechanism by which H-NS-mediated silencing can be reversed |CITS: [29473964]|. Based on proteomic studies, it was determined that the activities of nucleoid-associated proteins (NAPs) such as H-NS, HU, IHF, and FIS are also modulated by posttranslational modifications (PTMs) that signal differences in growth conditions; because none of the NAPs are known to bind any signaling ligands, these growth condition signals may be compensated for by these PTMs |CITS: [30287510]|. The negative supercoiling of DNA in Fis, H-NS, and HU transcription factors modulates their 3D shape and determines their molecular dynamics |CITS: [28191853]|. The circular supercoiled DNA dynamically folds in particular higher-order structures (hyperplectonemes) |CITS: [28191853]|. The architecture and structural and functional characteristics of analogs of H-NS found in other bacterial species that are able to bridge DNA duplexes (a key to genome compaction), gene regulation, and their response to changing conditions in the environment were reviewed |CITS: [31795918]|. Based on the Magnetic Tweezers technique, a cooperative effect was observed between H-NS activity and the depletion of forces induced by the crowding agent PEG|CITS:[32891648]|. Missense or insertion mutations in the hns gene compensate for a knockout mutation in the genes encoding the major antibiotic efflux pumps AcrAB and AcrEF through derepression of genes enconding the MdtEF efflux pump |CITS: [33972351]|. DrdX: "derepressed expression" |CITS: [1691451]| Reviews: |CITS: [16879983][17191074][15853876][9513262][15100692][12753181][27720010][27913665][26445432]|