Physiologically important stabilization of DNA by a prokaryotic histone-like protein

The thermophilic mycoplasma Thermoplasma acidophilum has tightly bound to its DNA a protein that closely resembles the histones of eukaryotes. DNA associated with this protein is more stable than free DNA against thermal denaturation by about 40 degrees C, as shown in both native nucleoprotein and in hybrid nucleoprotein reconstituted in vitro with calf DNA. Since only about 20 percent of the DNA in this organism is associated with the histone-like protein, we suggest that its physiological function is to prevent complete separation of the DNA strands during brief exposures of the organism to denaturing conditions, and thus to facilitate rapid renaturation when normal environmental conditions return.