Exonuclease VII of Escherichia coli: PURIFICATION AND PROPERTIES

Abstract

Abstract A new deoxyribonuclease, exonuclease VII, has been identified and purified 1,700-fold from Escherichia coli K12. The enzyme is an exonuclease specific for single-stranded DNA or duplex DNA containing single-stranded termini. The purified enzyme is active in the presence of EDTA, but is stimulated 25% by MgCl2. Optimal activity occurs at pH 7.9 in potassium phosphate buffer. The molecular weight, as determined by gel filtration and sedimentation analysis, is 88,000; the Stokes radius is 89 A. The friction coefficient of the enzyme is 3.07, suggesting an asymmetric structure. In the accompanying paper (Chase, J. W., and Richardson, C. C. (1974) J. Biol. Chem. 249, 4553–4561) we show that the enzyme is an exonuclease which can initiate hydrolysis at both 3' and 5' termini to yield products which are exclusively oligonucleotides.