A study of the genetic material determining an enzyme activity in Pneumococcus

An enzyme of Pneumococcus responsible for the conversion of maltose to glucose and oligosaccharides was investigated. The genetic analysis of a group of mutants lacking this enzyme was accomplished by studying DNA-mediated transformations of the different strains. Transformation of the different mutants to maltose utilization by wild-type DNA occurred with different frequencies. Recombination of genetic material of the maltose-negative strains also gave rise to positive cells. Analysis of the recombinations indicated that the regions corresponding to the different markers are linked and arranged in a linear fashion. Some larger regions overlapped several smaller ones indicating that single mutations altered regions in the genetic material of different size. Heating the DNA used in transforming the mutant strains destroyed most rapidly the ability to transform the factors corresponding to the larger genetic regions. Factors corresponding to smaller regions were inactivated less rapidly. This is taken to indicate that a DNA molecule partly denatured by heat still retains part of its genetic activity. It is concluded, furthermore, that genetic properties of markers, such as size, linkage, and discreteness, are reflections of the actual distribution of determinants within DNA molecules.