The structural and functional organization of H-NS-like proteins is evolutionarily conserved in Gram-negative bacteria

The structural gene of the H-NS protein, a global regulator of bacterial me tabolism, has been identified in the group of enterobacteria as well as in closely related bacteria, such as Erwinia chrysanthemi and Haemophilus infl uenzae. Isolated outside these groups, the BpH3 protein of Bordetella pertu ssis exhibits a low amino acid conservation with H-NS, particularly in the N-terminal domain. To obtain information on the structure, function and/or evolution of H-NS, we searched for other H-NS-related proteins in the lates t databases. We found that HvrA, a trans-activator protein in Rhodobacter c apsulatus, has a low but significant similarity with H-NS and H-NS-like pro teins. This Gram-negative bacterium is phylogenetically distant from Escher ichia coli. Using theoretical analysis (e.g. secondary structure prediction and DNA binding domain modelling) of the amino acid sequence of H-NS, StpA (an H-NS-like protein in E. coli), BpH3 and HvrA and by in vivo and in vit ro experiments (e.g. complementation of various H-NS-related phenotypes and competitive gel shift assay), we present evidence that these proteins belo ng to the same class of DNA binding proteins, in silico analysis suggests t hat this family also includes Spa in R. sphaeroides, XRVA in Xanthomonas or yzae and VicH in Vibrio cholerae. These results demonstrate that proteins s tructurally and functionally related to H-NS are widespread in Gram-negativ e bacteria.