The Specificity of Five DNAases as Studied by the Analysis of 5′‐Terminal Doublets

Abstract

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 (P̄_n) 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.