The bacterial DNA-binding protein H-NS represses ribosomal RNA transcription by trapping RNA polymerase in the initiation complex

The bacterial nucleoid: A highly organized and dynamic structure

“…The mechanism by which H-NS influences RNA polymerase activity is not fully understood. Its function as a transcription factor is, however, tightly connected with its ability to oligomerize [Rimsky et al, 2001] and condense DNA into stable nucleoprotein complexes [Schroder and Wagner, 2000;Dole et al, 2004;Prosseda et al, 2004], thereby occluding promoter regions or blocking transcription elongation. Recently, atomic force microscopy was used to visualize the effects of H-NS on DNA topology [Dame et al, 2000]: after initial binding at dispersed sites, H-NS assembles into patches of oligomers that interact with each other, thus bridging different DNA regions.…”

DNA looping-mediated repression by histone-like protein H-NS: specific requirement of Eσ70 as a cofactor for looping

“…H-NS binding (K d ) to these preferred sites, therefore, is only in the range of micromolar concentration (Fried 1989;Sonnenfield et al 2001), not vastly stronger than to the DNA with no curvature (Lucht et al 1994). It has been suggested that initial binding of H-NS to a preferred site is followed by lateral extension along the DNA, by oligomerization of H-NS through interactions between N-terminal domains of the protein (Dorman et al 1999;Badaut et al 2002;Schroder and Wagner 2002). Scanning force microscopy has shown that the preferential binding to curved DNA fragments occurs as a result of the DNA around the curve being bridged by oligomeric H-NS, which leads to the formation of a hairpin-like structure (Dame et al 2001).…”

“…The oligomerization of H-NS is, therefore, essential for preferential binding and stabilization of the multimeric nucleoprotein complex (Spurio et al 1997). A recent study of an E. coli ribosomal gene promoter rrnB P1 has suggested that repression involves DNA looping and that the loop is closed by the association of two patches of H-NS-bound DNA in which the RNP is trapped, instead of being excluded (Schroder and Wagner 2000;Dame et al 2002;Dame 2005;Gralla 2005). According to this model, expression from an H-NS repressed promoter should require disruption of the nucleoprotein complex and the DNA loop by transcription factors.…”

The Degree of Oligomerization of the H-NS Nucleoid Structuring Protein Is Related to Specific Binding to DNA

“…In some well characterized cases, it exerts its action at the level of transcription, either alone or in conjunction with its paralog StpA (3,4). Both genetic and biochemical studies indicate that in this instance regulation of transcription is not mediated by a classical local interaction of H-NS with a canonical DNA sequence but rather that H-NS constitutes specific assemblies on the DNA that invade the promoter and prevent the formation of an efficient active complex between RNA polymerase and the DNA sequence (5)(6)(7)(8). The extent of repression is also markedly sensitive to external conditions such as temperature (9), growth phase control (10,11), or osmotic regulation (12)(13)(14).…”

“…Finally, the association-dissociation equilibrium of wild-type H-NS in solution was analyzed under our experimental conditions and qualitatively compared with the behavior of several altered proteins. 6 -tagged H-NS proteins were expressed in E. coli BL21 DE3 as described by Williams et al (23). Bacteria were harvested by centrifugation, resuspended in 30 ml of buffer A (40 mM phosphate buffer, pH 8.0, 0.5 M NaCl, 70 mM imidazole, and 1 mM pefabloc (Pentapharm)), and ruptured using a French press.…”