Gene 5.5 protein of bacteriophage T7 inhibits the nucleoid protein H-NS of Escherichia coli.

Gene 5.5 of coliphage T7 is one of the most highly expressed genes during T7 infection. Gene 5.5 protein, purified from cells overexpressing the cloned gene, purifies with the nucleoid protein H-NS of Escherichia coli during three chromatographic steps. A fusion protein of gene 5.5 protein and maltose binding protein also purifies with H-NS. The fusion protein binds to the DNA-H-NS complex and abolishes H-NS-mediated inhibition of transcription by Escherichia coli and T7 RNA polymerases in vitro. Expression of gene 5.5 also relieves the repression of the Escherichia coli proU promoter by H-NS in vivo. The change of leucine to proline at residue 30 of gene 5.5 protein abolishes the interaction between gene 5.5 protein and H-NS.