Coordinated and differential expression of histone-like proteins in Escherichia coli: regulation and function of the H-NS analog StpA.

The histone-like protein H-NS has been shown to influence the regulation of gene expression at the transcriptional level in several Escherichia coli operons. We have examined the regulation of the stpA gene, which encodes a protein sharing 58% identity with H-NS, by mRNA analysis and by using stpA-lacZ operon fusions. The expression of stpA is temperature dependent, with 2-fold higher expression at 37 degrees C than at 26 degrees C. In addition, stpA expression is stimulated by the global regulator Lrp. In an hns mutant E.coli derivative stpA expression is derepressed, suggesting that regulation of the two genes is coupled. Overproduction of the StpA protein affects expression from at least four hns regulated operons (the papB, proU, bgl and hns operons), in both the presence and absence of H-NS. The construction of E.coli strains carrying mutations in both stpA and hns demonstrated that the absence of both proteins affects growth rate and viability of the cells. Our work establishes that E.coli can express two H-NS-like proteins with coordinated yet differential regulation. Evidently, these proteins have both overlapping and distinct functions in the cell, and they are both important for normal cell growth and gene control.