Abstract
Alterations in the transforming activity of deoxyribonucleic acid (DNA) from Diplococcus pneumoniae, type III, subsequent to gamma-irradiation were investigated. When DNA is irradiated in saline, doses of the order of 10,000 to 20,000 rep result in a significant decrease in transforming activity; complete inactivation is achieved at 40,000 rep. Much greater intensities are required to inactivate DNA irradiated in 0.5% cysteine solution. Transforming activity was demonstrated in DNA preparations exposed to 250,000 rep. Highly active transforming principle was isolated from cells exposed to radiation doses that have a marked effect on cell survival.