SELECTIVE HEAT INACTIVATION OF PNEUMOCOCCAL TRANSFORMING DEOXYRIBONUCLEATE

Abstract

Pneumococcal transforming DNA after heat inactivation shows two very different selective inactivation patterns for 5 drug-resistance markers, reflecting two different inactivation processes. When DNA is heated briefly at successively higher temperatures, a critical inactivation occurs, different genetic markers being inactivated at different characteristic critical temperatures. Heating for extended periods of time at subcritical temperatures results in a slow inactivation (presumably depurination) with different genetic markers being inactivated at different rates. When correlation is made with the physical changes as well as with the behavior of linked and unlinked groups of genetic markers, the conclusion is drawn that the critical inactivation process involves a physical collapse of entire molecules and linkage groups, while the subcritical inactivation involves the damage of small regions within molecules, selectivity depending upon their relative size. The kinetics of the two types of inactivation allow separation of the processes by the proper choice of the time and temperature of heating. The structural map of the DNA markers derived in this way is consistent with the known genetic map of these markers.