Mung Bean Nuclease I III . PURIFICATION PROCEDURE AND ( 3 ’ ) ~ o - MONOPHOSPHATASE ACTIVITY

A method leading to partial purification of mung bean nuclease I (potency 250) in good yield is described. Mung bean nuclease I of potency 1800 was obtained in small yield. At this stage the preparation showed two bands on disc electrophoresis. Throughout all stages of purification the nuclease activity was accompanied by (3’)~w-monophosphatase activity, suggesting that both activities are intrinsic properties of the same enzyme molecule. Dinucleotides dNpNp were first dephosphorylated by this enzyme to dNpN; then the internucleotide linkage was cleaved to form dN + dpN. The w-monophosphatase hydrolyzes ribose mononucleotides 50to loo-fold faster than the corresponding deoxyribose compounds. It also shows preference for bases, the order agrees with that previously established for the nuclease activity: A > T(U) > C > G. For the nuclease activity one exception was noted, ribopoly U was hydrolyzed faster than ribopoly A, presumably because the former lacks an ordered structure.