Characterization of a novel, low-molecular-weight DNA-binding protein from Escherichia coli.

A low-molecular-weight (7000), heat-stable protein--HU--that stimulates transcription of bacteriophage lambda DNA by E. coli RNA polymerase was purified from E. coli extracts using affinity chromatography on DNA-cellulose. HU binds to native DNA, resulting in an apparent thickening of the DNA chains as revealed by electron microscopy. Contrary to DNA unwinding proteins, it causes no destabilization of the double helix. HU differs from previously described transcription factors (H1, D, etc.) and from the low-molecular-weight omega subunit of the RNA polymerase. By its amino-acid composition and characteristics, HU displays an interesting resemblance to some eukaryotic histones, such as H2B and H1.