Purification and Characterization of a DNA-binding protein for Nucleoid Structure of Escherichia coli

A 22,000-dalton DNA-binding protein has been purified to apparent homogeneity from the cells of an Escherichia coli K-12 strain. The protein binds to the superhelical DNA molecule with a protein to DNA weight ratio of 3 to 2. The protein showed the high affinity to the single-stranded DNA molecule and the lower affinity to the linear duplex DNA molecule. The amino acid composition of the protein resembled those of the other prokaryotic histone-like proteins and eukaryotic histone H2A. The protein was heat labile unlike other histone-like proteins. In addition, DNA, RNA and protein syntheses in vitro were not affected by the presence of the protein. In view of these features, this protein may play a role in maintaining the bacterial nucleoid structure.