The 5.5 protein of phage T7 inhibits H-NS through interactions with the central oligomerization domain

J Bacteriol. 2011 Sep;193(18):4881-92. doi: 10.1128/JB.05198-11. Epub 2011 Jul 15.


The 5.5 protein (T7p32) of coliphage T7 (5.5(T7)) was shown to bind and inhibit gene silencing by the nucleoid-associated protein H-NS, but the mechanism by which it acts was not understood. The 5.5(T7) protein is insoluble when expressed in Escherichia coli, but we find that 5.5(T7) can be isolated in a soluble form when coexpressed with a truncated version of H-NS followed by subsequent disruption of the complex during anion-exchange chromatography. Association studies reveal that 5.5(T7) binds a region of H-NS (residues 60 to 80) recently found to contain a distinct domain necessary for higher-order H-NS oligomerization. Accordingly, we find that purified 5.5(T7) can disrupt higher-order H-NS-DNA complexes in vitro but does not abolish DNA binding by H-NS per se. Homologues of the 5.5(T7) protein are found exclusively among members of the Autographivirinae that infect enteric bacteria, and despite fairly low sequence conservation, the H-NS binding properties of these proteins are largely conserved. Unexpectedly, we find that the 5.5(T7) protein copurifies with heterogeneous low-molecular-weight RNA, likely tRNA, through several chromatography steps and that this interaction does not require the DNA binding domain of H-NS. The 5.5 proteins utilize a previously undescribed mechanism of H-NS antagonism that further highlights the critical importance that higher-order oligomerization plays in H-NS-mediated gene repression.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacteriophage T7 / physiology*
  • Escherichia coli / physiology*
  • Escherichia coli / virology*
  • Escherichia coli Proteins / metabolism*
  • Fimbriae Proteins / metabolism*
  • Protein Binding
  • Protein Interaction Mapping*
  • Protein Structure, Tertiary
  • Viral Proteins / metabolism*


  • Escherichia coli Proteins
  • FimG protein, E coli
  • Viral Proteins
  • gene 5.5 protein, Bacteriophage T7
  • Fimbriae Proteins