The incomplete denaturation of DNA in N,N-dimethyl formamide.

In this paper we show that the extent of DNA denaturation achieved by dialysis against N,N-dimethyl formamide depends on both the source of DNA and the buffer used. The stability against denaturation increases with the guanine plus cytosine content. The base sequence also plays a minor role. This behavior is due to differences in the solubility of DNA in the denaturing solvent. The DNAs with a high guanine-cytosine content have a lower solubility in dimethyl formamide and this fact results in a higher stability against denaturation. As a practical consequence, in order to achieve complete denaturation of DNA by dialysis against dimethyl formamide, it is necessary to start with DNA dissolved in a buffer of low ionic strength, preferably below 10(-3) M.