High‐order oligomerization is required for the function of the H‐NS family member MvaT in Pseudomonas aeruginosa

H‐NS is an abundant DNA‐binding protein that has been implicated in the silencing of foreign DNA in several different bacteria. The ability of H‐NS dimers to form higher‐order oligomers is thought to aid the polymerization of the protein across AT‐rich stretches of DNA and facilitate gene silencing. Although the oligomerization of H‐NS from enteric bacteria has been the subject of intense investigation, little is known regarding the oligomerization of H‐NS family members from bacteria outside of the enterobacteriaceae, many of which share little sequence similarity with their enteric counterparts. Here we show that MvaT, a member of the H‐NS family of proteins from Pseudomonas aeruginosa, can form both dimers and higher‐order oligomers, and we identify a region within MvaT that mediates higher‐order oligomer formation. Using genetic assays we identify mutants of MvaT that are defective for higher‐order oligomer formation. We present evidence that these mutants are functionally impaired and exhibit DNA‐binding defects because of their inability to form higher‐order oligomers. Our findings support a model in which the ability of MvaT to bind efficiently to the DNA depends upon protein–protein interactions between MvaT dimers and suggest that the ability to form higher‐order oligomers is a conserved and essential feature of H‐NS family members.