A DNA-binding protein implicated in transcriptional repression (silencing) (PubMed:333393, PubMed:2128918, PubMed:8890170, PubMed:8913298, PubMed:9398522, PubMed:16963779, PubMed:17046956, PubMed:23543115). Also involved in bacterial chromosome organization and compaction (PubMed:6379600, PubMed:10982869, PubMed:21903814). H-NS binds tightly to AT-rich dsDNA and inhibits transcription (PubMed:2512122, PubMed:16963779, PubMed:17435766, PubMed:17881364, PubMed:23543115). Binds upstream and downstream of initiating RNA polymerase, trapping it in a loop and preventing transcription (PubMed:11714691). Binds to hundreds of sites, approximately half its binding sites are in non-coding DNA, which only accounts for about 10% of the genome (PubMed:16963779, PubMed:17046956, PubMed:23543115). Many of these loci were horizontally transferred (HTG); this offers the selective advantage of silencing foreign DNA while keeping it in the genome in case of need (PubMed:17046956, PubMed:17881364, PubMed:26789284). Suppresses transcription at many intragenic sites as well as transcription of spurious, non-coding RNAs genome-wide (PubMed:24449106). Repression of HTG by H-NS is thought to allow their DNA to evolve faster than non-H-NS-bound regions, and facilitates integration of HTG into transcriptional regulatory networks (PubMed:26789284). A subset of H-NS/StpA-regulated genes also require Hha (and/or Cnu, ydgT) for repression; Hha and Cnu increase the number of genes DNA bound by H-NS/StpA and may also modulate the oligomerization of the H-NS/StpA-complex (PubMed:23543115). The protein forms 2 clusters in the nucleoid which gather hns-bound loci together, bridging non-contiguous DNA, and causes DNA substantial condensation (PubMed:21903814). Binds DNA better at low temperatures than at 37 degrees Celsius; AT-rich sites nucleate H-NS binding, further DNA-binding is cooperative and this cooperativity decreases with rising temperature (PubMed:17435766, PubMed:17881364). Transcriptional repression can be inhibited by dominant-negative mutants of StpA or itself (PubMed:8755860). May affect transcriptional elongation (PubMed:25638302). Can increase translational efficiency of mRNA with suboptimal Shine-Dalgarno sequences (PubMed:20595230). Plays a role in the thermal control of pili and adhesive curli fimbriae production, by inducing transcription of csgD (PubMed:17010156). Plays a role in flagellar function (PubMed:11031114). Represses the CRISPR-cas promoters, permits only weak transcription of the crRNA precursor; its repression is antagonized by LeuO (PubMed:20132443, PubMed:20659289). Binds preferentially to the upstream region of its own gene recognizing two segments of DNA on both sides of a bend centered around -150 (PubMed:7934818). Overexpression suppresses secY24, a temperature-sensitive mutation (PubMed:1537791). Has also been reported to activate transcription of some genes (PubMed:4566454, PubMed:338303, PubMed:2128918). Hydroxyisobutyrylation on Lys-121 (K121hib) decreases the DNA-binding activity of H-NS, promotes the expression of acid-resistance genes and enhances bacterial survival under extreme acid stress. Homodimer, also found as tetramers or higher oligomers (PubMed:4566454, PubMed:338303, PubMed:3135462, PubMed:8913298, PubMed:9398522, PubMed:8755860, PubMed:12460581, PubMed:23601147). Oligomerizes into higher-order complexes that form bridges between adjacent DNA helices. The N-terminal region (residues 1-64) can interact with overexpressed StpA (PubMed:8755860). Forms a complex with Cnu (YdgT) (PubMed:21600204). The H-NS dimer forms a heterotrimeric complex with Hha in the absence of DNA; this is mediated by residues 1-46 (PubMed:21600204, PubMed:11790731, PubMed:16650431, PubMed:26085102). Interacts with Hfq (PubMed:2020545). Forms 2 compact clusters per chromosome, located at one-quarter and three-quarter positions on the cell's long axis: 2 H-NS-repressed genes were closely associated with H-NS clusters while a non-H-NS-repressed gene was not substantially associated with the H-NS cluster (PubMed:21903814). Protein levels rise from about 4,000/cell in exponential phase to about 18,000/cell in late stationary phase (at protein level) (PubMed:6379600). Subject to transcriptional auto-repression (PubMed:7934818). Induced by increased hydrostatic pressure (PubMed:8226663). hns transcription can be repressed by overexpressed StpA (which is usually repressed by hns) (PubMed:8890170). Induced by cold shock (42 to 15 degrees Celsius) (at protein level) (PubMed:8898389). A central region (about residues 21-47) is involved in dimerization, but multimerization requires other residues (PubMed:8755860, PubMed:9398522, PubMed:16650431, PubMed:12460581, PubMed:12592399). The dimerization domain (1-47) also acts as a hinge; changes in its structure probably impact oligomerization and DNA-binding geometries (PubMed:23601147). The N-terminus also interacts with Hha, perhaps via residues 2-18; a well-folded dimer is not necessary for Hha binding (PubMed:16650431). The C-terminus (residues 92-137) binds DNA (PubMed:8913298). Residues in the N-terminus contribute to DNA-binding and to discrimination between curved and non-curved DNA (PubMed:12592399). 2-hydroxyisobutyrylated by TmcA on Lys-121. Cells (strain MRE-600) in mid-exponential phase have three 15.5 kDa proteins with 3 different isoelectric points; the major form (H1a, pI 7.5) rises in concentration during growth while the 2 minor forms (H1b, pI about 7.2 and H1c, pI 7.0) remain approximately constant (PubMed:6379600). A second experiment gave a mass of 15410.1. Decreased growth below 30 degrees Celsius (PubMed:1691451). Altered expression of a number of genes (PubMed:2128918, PubMed:8890170, PubMed:8913298, PubMed:23543115). Derepression of the cryptic blg operon (PubMed:8913298, PubMed:11790731). Alteration of chromosome organization (PubMed:21903814). Double hns-stpA mutants grow slower and have reduced viable cell counts compared to single hns mutants in MC1029 and MC4100 backgrounds (PubMed:8890170). In 0.3M NaCl a double hns-stpA deletion up-regulates 583 and down-regulates 86 genes, 363 of which are thought to have been horizontally acquired; 131 are also up-regulated in a double cnu-hha deletion (PubMed:23543115). At 28 degrees Celsius csgD transcription is reduced (PubMed:17010156). Flagella loss due to reduced expression of the flhDC operon (PubMed:11031114). Flagella can be restored by expression of flhDC, but strains are non-motile, suggesting H-NS also plays a role in flagellar function (PubMed:11031114). Disruption leads to increased expression of CRISPR-cas genes and increased viral resistance (PubMed:20659289). Belongs to the histone-like protein H-NS family.