Histone-like protein H1 (H-NS), DNA supercoiling, and gene expression in bacteria.

Changes in DNA supercoiling in response to environmental signals such as osmolarity, temperature, or anaerobicity appear to play an underlying role in the regulation of gene expression in bacteria. Extensive genetic analyses have implicated the osmZ gene in this regulatory process: osmZ mutations are highly pleiotropic and alter the topology of cellular DNA. We have shown that the product of the osmZ gene is the "histone-like" protein H1 (H-NS). Protein H1 is one of the most abundant components of bacterial chromatin and binds to DNA in a relatively nonspecific fashion. These data imply a regulatory role for one of the major components of bacterial chromatin and provide support for the notion that changes in DNA topology and/or chromatin structure play a role in regulating gene expression.