Oligomerization of the chromatin-structuring protein H-NS

H-NS is a major component of the bacterial nucleoid, involved in condensing and packaging DNA and modulating gene expression. The mechanism by which t his is achieved remains unclear. Genetic data show that the biological prop erties of H-NS are influenced by its oligomerization properties. We have ap plied a variety of biophysical techniques to study the structural basis of oligomerization of the H-NS protein from Salmonella typhimurium. The N-term inal 89 amino acids are responsible for oligomerization. The first 64 resid ues form a trimer dominated by an alpha-helix, likely to be in coiled-coil conformation. Extending this polypeptide to 89 amino acids generated higher order, heterodisperse oligomers. Similarly, in the full-length protein no single, defined oligomeric state is adopted. The C-terminal 48 residues do not participate in oligomerization and form a monomeric, DNA-binding domain . These Nand C-terminal domains are joined via a flexible linker which enab les them to function independently within the context of the full-length pr otein. This novel mode of oligomerization may account for the unusual bindi ng properties of H-NS.