The specificity of five DNAases as studied by the analysis of 5'-terminal doublets

The 5'-terminal dinucleotides released by five deoxyribonucleases (spleen acid DNase, snail acid DNase, pancreatic DNase, Escherichia coli endonuclease I and crab DNase) have been determined on E. coli DNA (51% dG & dC) digests having different average sizes (Pn) in the range 50 to 10. It has been shown that the composition of the 5'-terminal dinucleotide (a) is independent upon the degradation level, at least in the range explored; (b) is strongly different from the composition of E. coli DNA doublets, these differences being characteristic for each enzyme; (c) is very significantly different from the statistical composition of 5'-terminal dinucleotides, as calculated from the composition of 5'-terminal and penultimate nucleotides. A calculation of the statistical composition of the trinucleotides split by each enzyme, using the 3'-terminal nucleotide data in conjunction with the 5'-terminal dinucleotide results provided a qualitative "specificity spectrum" for each enzyme.