NOTES DNA Bridging: a Property Shared among H-NS-Like Proteins

The nucleoid-associated protein H-NS is thought to play an essential role in the organization of bacterial chromatin in Escherichia coli. Homologues, often with very low sequence identity, are found in most gram-negative bacteria. Microscopic analysis reveals that, despite limited sequence identity, their structural orga-nization results in similar DNA binding properties. The chromosomal DNA of bacteria is organized into a com-pact structure, the nucleoid. A number of factors contribute to maintaining this compact state: macromolecular crowding (or depletion), DNA supercoiling, and so-called nucleoid-associ-ated proteins (28). It is unclear how much each of these factors contributes to nucleoid compactness, but nucleoid-associated proteins play an essential role. Important members of this group of proteins are H-NS, HU, Fis, and integration host factor (IHF) (12, 18). In addition to a role in compaction, these proteins act as specific regulators (for instance in transcrip-tion). Both HU (27) and IHF (1) reduce the effective volum