An extracellular deoxyribonuclease separated from Streptococcus sanguis I destroyed the thymus DNA and then produced mono-, di-, tri-, tetra- and other oligonucleotides.

These oligonucleotides were determined by the combination of Sephadex G-25 gelfiltration and DEAE-Sephacel ion exchange chromatography in the presence of 7M urea.

The results were summarized as follows:

Only thymus DNA was hydrolyzed by the DNase and its molecular weight decreased to 2.2 x 10⁵daltons on 0.8% agarose gel electrophoresis. However, the DNase showed no enzymatic activity for λ phage DNA, fd phage DNA, thermally denatured thymus DNA or themally denatured thymus λDNA.

It suggests that the DNase has high specific activity for native thymus DNA.