Thermal renaturation of deoxyribonucleic acids

Abstract

The conditions that produce the optimal re-formation of the native DNA conformation from denatured DNA have been examined. The restoration of the native conformation, called thermal renaturation, has been found to depend markedly on the source of the DNA; mammalian DNA coming from cells with very large DNA content renatures only slightly, bacterial DNA with greatly reduced DNA content per cell undergoes extensive renaturation, and the very smallest bacteria together with bacteriophage, having the lowest DNA contents, show nearly complete renaturation. With a given DNA, the optimal renaturation was found to occur at about 25° below the denaturation temperature, T m . The extent of renaturation was optimal above 0·4 M -Na + and increased with molecular weight. The identity of the renatured DNA and the native material can be shown in two ways: the similarity of the absorbance-temperature curves and the similarity of the rate of thermal inactivation of biological markers at temperatures somewhat above T m . This reproduceability of the helix-coil transition and the course of thermal inactivation demonstrates that the same secondary structure has re-formed and that non-specific hydrogen bonding is not involved.