Large-scale monitoring of pleiotropic regulation of gene expression by theprokaryotic nucleoid-associated protein, H-NS

Despite many years of intense work investigating the function of nucleoid-a ssociated proteins in prokaryotes, their role in bacterial physiology remai ns largely unknown. The two-dimensional protein patterns were compared and expression profiling was carried out on H-NS-deficient and wild-type strain s of Escherichia coil K-12. The expression of approximately 5% of the genes and/or the accumulation of their protein was directly or indirectly altere d in the hns mutant strain. About one-fifth of these genes encode proteins that are involved in transcription or translation and one-third are known t o or were in silico predicted to encode cell envelope components or protein s that are usually involved in bacterial adaptation to changes in environme ntal conditions. The increased expression of several genes in the mutant re sulted in a better ability of this strain to survive at low pH end high osm olarity than the wildtype strain. In particular, the putative regulator, Yh iX, plays a central role in the H-NS control of genes required in the gluta mate-dependent acid stress response. These results suggest that there is a strong relationship between the H-NS regulon and the maintenance of intrace llular homeostasis.