摘要：

The loss of capacity of pneumococcal DNA to effect transformation as the result of exposure to several degradative agents has been studied, together with the concomitant decline in cellular incorporation of the treated DNA. The results indicate a one-hit process for the loss of genetic activity, and are in accord with the hypothesis that cellular incorporation reflects the number average molecular weight of the DNA. On this basis it has been possible to define the length of a critical DNA segment essential to genetic activity. Its value for the traits studied is about 8% of the intact molecule.Treatment by heat or ultraviolet yields multicomponent inactivation curves. The former appears to be the result of two easily distinguishable processes. Of all the agents tested, only ultraviolet discriminated between the optochin and streptomycin resistance markers. The quantum yield for ultraviolet inactivation has been calculated.

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