Studies on bovine pancreatic deoxyribonuclease A: II. The effect of different bivalent metals on the specificity of degradation of DNA

Abstract

The specificity of deoxyribonuclease A has been shown to vary according to the bivalent metal used for activation of the enzyme. Examination of the 5′- and 3′-terminal nucleosides of oligonucleotides released by deoxyribonuclease A from Escherichia coli K12 and calf thymus DNA after partial, intermediate or extensive periods of hydrolysis has shown that changes in specificity of the enzyme also occur with time during the hydrolysis. The change in specificity was observed only when the enzyme was activated by certain bivalent metal ions and the ions have been divided into two groups. With each ion of Group A, which includes Cd 2+, Ca 2+, Ba 2+, Co 2+ and Mg 2+ plus Ca 2+, distribution of terminal nucleosides of oligonucleotides released by deoxyribonuclease at any period of hydrolysis was the same, the specificity of the enzyme thus remaining constant. With each bivalent metal of Group B, Mg 2+, Mn 2+, Ni 2+, Sr 2+ and Zn 2+, the distribution of terminal nucleosides of oligonucleotides released by deoxyribonuclease A when partial and extensive hydrolysates of DNA were compared was different. Knowledge of the nucleoside termini of mono-, di- and trinucleotides alone only gives partial information on specificity. Total hydrolysates or oligonucleotides of various chain length indicated that deoxyribonuclease activated by Mg 2+, Sr 2+ and Ni 2+ and probably all ions of Group B can be used to isolate certain oligonucleotides lacking dA at the 3′ end. This observation may be of use in sequence studies on DNA.