Horizontally acquired homologues of the nucleoid-associated protein H-NS: implications for gene regulation.

H-NS is one of the most intensively studied members of the family of bacterial nucleoid-associated proteins. It is a DNA-binding protein with a preference for A+T-rich DNA sequences, and it represses the transcription of hundreds of genes in Gram-negative bacteria, including pathogens. In most cases where the issue has been investigated, the repressive activity of H-NS is opposed by the intervention of an antagonistically acting DNA-binding protein, a remodelling of local DNA structure, or a combination of these two. H-NS activity can also be modulated by protein-protein interaction with members of the Hha/YdgT protein family, molecules that share partial amino acid sequence similarity to the oligomerization domain of H-NS. Of particular interest is the ability of H-NS to interact with the full-length paralogue StpA or full-length orthologues that have been acquired by horizontal DNA transfer. In this issue of Molecular Microbiology, Müller et al. describe the H-NS orthologue Hfp and present evidence that in bacteria that acquire Hfp the range of activities of H-NS is modified with important implications for the physiology of the bacterium.