The Specificity of Pancreatic Deoxyribonuclease

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Abstract
The kinetics of degradation of calf thymus DNA by pancreatic DNAase has been investigated with the main purpose of providing the background for studying the specificity of the enzyme and its use in investigations of nucleotide sequences in DNA. The relationships between the hyperchromic shift or acid solubility and the reciprocal average degree of polymerization (P̄n−1) of the hydrolysate have been established; these can be used in order to prepare oligonucleotides of desired average chain length simply by measuring the increase of absorbance or of acid solubility of the digest during DNA degradation.The specificity of the pancreatic DNAase was studied by determining the base compositions of 3′‐terminal, 5′‐terminal and 5′‐penultimate nucleotides of oligonucleotides released by the enzyme. The 3′‐terminal nucleotide composition was found not to vary in the P̄n, or average size, range 150 to 8 and 30 to 8 for digestions of calf thymus DNA in the presence of magnesium and manganese ions, respectively, indicating that no change in the specificity takes place during digestion. The compositions of 3′‐terminal, 5′‐terminal and 5′‐penultimate nucleotides differ from those expected on the basis of random splitting of DNA. The conclusion is drawn that pancreatic DNAase recognizes sequences at least three nucleotides long.