Histone-like nucleoid-structuring protein

[2] Though it is a small protein (15 kDa),[3] it provides essential nucleoid compaction and regulation of genes (mainly silencing)[2] and is highly expressed, functioning as a dimer or multimer.

[3] Change in temperature causes H-NS to be dissociated from the DNA duplex, allowing for transcription by RNA polymerase, and in specific regions lead to pathogenic cascades in enterobacteria such as Escherichia coli and the four Shigella species.

[3] H-NS has a specific topology that allows it to condense bacterial DNA into a superhelical structure based on evidence from X-ray crystallography.

[3] The process for formation of H-NS-DNA complexes begins with the CTD binding to a preferential site in the genome.

This may be the result of the large amount of positively charged amino acid residues located within the linker region that causes the CTD to search for a binding site with high affinity.

[2] The experiments used to support this method of DNA binding and gene silencing come from Atomic Force Microscopy and single-molecule studies in vitro.

[9] The charges seen in the NTD and CTD may explain how H-NS remains sensitive to changes in temperature and osmolarity (pH below 7.4).

[6] H-NS has a conserved role in the pathogenicity of gram-negative bacteria including Shigella spp., Escherichia coli, Salmonella spp., and many others.

[10] Interestingly, almost 70% of the open reading frames (ORF) of the specialized virulence plasmid in Shigella spp.

contain "molecular backups", or paralogues, to H-NS that have been studied in detail due to their apparent assistance in organization of the virulence plasmid.

[3] StpA is a paralogue of H-NS that is conserved across the species but the other, Sfh is expressed solely in the S. flexneri mutant strain 2457T.

Figure 1: The C-terminal domain (CTD) [ 4 ] is also known as the DNA-binding domain. H-NS NTD's oligomerize with each other while the CTD binds to specific regions of DNA containing a specific topology called a TpA step. [ 2 ] Aromatic amino acid residues are labelled in gray, negatively charged particles are displayed in red, and positively charged particles are labelled in teal. H-bond lengths are displayed in magenta.
Figure 2 : This figure portrays the oligomerization occurring in the alpha helices of the NTD in H-NS (and homologues) forming what is known as a "handshake topology" and an estimated view of how the CTD binds to DNA. [ 2 ]
Figure 3 : (A) Illustration of the association of H-NS to S. flexneri DNA at 32°C and then when temperature reaches 37°C, H-NS dissociates from the DNA, allowing for the transcription of virF. (B) Further down the DNA duplex, the expression of VirB causes a disruption in silencing of icsB by H-NS and the cascade can continue causing wide-spread infection. [ 3 ]