Genetic transformation I. Cellular incorporation of DNA accompanying transformation in Pneumococcus

Abstract

The incorporation of 32P-labeled DNA by pneumococcal cells undergoing genetic transformation has been studied. While acceptibility for incorporation is not limited to genetically active DNA nor to pneumococcal DNA, neither RNA nor severely degraded DNA are significantly incorporated. The frequency of transformation among cells presented with genetically active pneumococcal DNA is directly proportional to the amount of DNA incorporated. This proportionality holds upon variation of any of a number of experimental conditions, including temperature and duration of exposure, concentration of DNA, and presence of inhibiting DNA. The quantitative relationships indicate that only a fraction of the incorporated DNA may be functional in the usual sense; about 2-10 times the normal cellular content of DNA is incorporated per transformation to streptomycin resistance. They also suggest that the DNA is first bound in a temporary, perhaps superficial state, from which either expulsion or permanent incorporation proceeds. Slight previous degradation by DNase reduces incorporation and genetic activity at different rates, the latter much more rapidly. © 1957.