ORIGIN OF RESIDUAL TRANSFORMING ACTIVITY OF DENATURED BACILLUS SUBTILIS DNA

Assays of the transforming activity of fractions obtained from a density-gradient of thermally denatured Bacillus subtilis DNA show that the residual activity is located away from the bulk of the DNA (denatured) and at densities corresponding to native or nearly native DNA. By using biologically formed hybrid DNA in which one strand has an enhanced density, it is shown that the two strands of the molecules bearing the residual activity do not separate under denaturing conditions. Thus the residual transforming activity of this DNA (1 to 4%) is due to a denaturation-resistant fraction. The inactive, denatured DNA is not taken up by competent cells, unless it is converted to the bihelical form by renaturation, in which case about 40% of the transforming activity of native DNA is restored. © 1968.