Apparent thermal destabilization of Escherichia coli nucleoprotein due to the incomplete dialysis of EDTA.

Escherichia coli nucleoprotein has been found to undergo thermal denaturation approx. 5 degrees C lower than purified E. coli DNA, measured in 0.25 mM sodium EDTA, pH 8.0 (Searcy, D.G. (1975) Biochim. Biophys. Acta 395, 535-547). This is now shown to be an artifact due to the impermeability of dialysis membranes to sodium EDTA, especially at low concentrations such as 1 mM or less. Thermal denaturation data can be corrected by measuring the electrical conductivity of the solutions. When this is done, the nucleoprotein and DNA both denature at the same temperature.