to influence DNA topology (Figure 2). H-NS is responsible for formation of nucleofilaments along the DNA and DNA-DNA bridges. H-NS is known as a passive DNA bridger, meaning that it binds two distant segments of DNA and remains stationary, forming a loop. This DNA loop formation allows H-NS to control gene expression. Relief of suppression by H-NS can be achieved by the binding of another protein, or by changes in DNA topology which can occur due to changes in temperature and osmolarity, for example. The CTD binds to the bacterial DNA in such a way that inhibits the function of RNA polymerase. This is a common feature seen in horizontally acquired genes. Structural studies of H-NS use bacterial species such as E. coli and Shigella spp. because the C-Terminal Domain is completely conserved. 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. Once the CTD is bound to its preferential region, TpA step, the NTD's can oligomerize and form rigid nucleofilaments that, if favorable conditions exist, will more freely bind to one another to form DNA-bridges. This form of bridging is known as "passive bridging" and may not allow RNAP to proceed with transcription. The experiments used to support this method of DNA binding and gene silencing come from Atomic Force Microscopy and single-molecule studies in vitro. All bacteria must be sensitive to changes in their physical environment to survive. These mechanisms allow for turning genes on or off depending on its extracellular environment. Many researchers believe that H-NS contributes to these sensory functions. H-NS has been observed to control around 60% of the temperature regulated genes and can dissociate from the DNA duplex at 37°C. This particular sensitivity seen in H-NS allows for pathogenesis and is the main focus of study. Outside of a host, the temperature of 32°C prevents dissociation of H-NS from the virulence plasmid in Shigella spp. in order to conserve energy for energetically costly production of proteins involved in pathogenesis. The presence of magnesium ions (Mg2+) has been shown to allow H-NS to form a slightly open to completely open conformational change in structure that will ultimately alter the interaction between the