Characterization of BpH3, an H-NS-like protein in Bordetella pertussis

This study describes the characterization of BpH3, a Bordetella pertussis DNA-binding protein. Sequence analysis reveals significant homology with the H-NS sequence of Escherichia coli and Haemophilus influenzae, particularly in the C-terminal part of the proteins. Our results provide evidence that H-NS and BpH3 display functional homology. First, expression of BpH3 in an hns mutant results in restoration of motility, an H-NS-dependent phenotype. This effect is dependent on the level of BpH3 expression and results from transcriptional activation of the flagellar master operon. Second, the high level of beta-glucosidase associated with hns mutations is reversed to the low wild-type level in the presence of BpH3. Third, BpH3 is able, like H-NS, to preferentially bind in vitro to curved DNA fragments, such as flhDC and bla promoter regions. Our results are the first demonstration that proteins homologous to H-NS exist in bacteria phylogenetically distant from H. influenzae and enterobacteria.