Some new applications of micrococcal nuclease to the elucidation of the structure of nucleic acids

In order to obtain more information on the specificity of micrococcal nuclease (EC 3.1.4.7), three series of substances were investigated:

• 1.

  1. The series of polypyrimidine nucleotides terminated at both ends by phosphoryl groups obtained by controlled hydrolysis of DNA.

• 2.

  2. Polythymidylic acids obtained by chemical synthesis.

• 3.

  3. Three naturally occuring deoxyribonucleic acids.

Using catalytic amounts of highly purified enzyme, it was shown that tri- and tetranucleotides are attacked with the liberation of the 3′-terminal nucleoside and (or) nucleotide in a stepwise manner. With pentanucleotides, exonucleolytic and endonucleolytic mechanisms of hydrolysis occur at the same rate. The fact that the enzyme attacks preferentially thymine and adenine linkages has been confirmed by using deoxyribonucleic acids containing different adenine-thymine ratios.