Purification and Properties of Adenosine 5'-Triphosphate-Dependent Deoxyribonuclease from Thermus thermophilus HB8

Abstract

An ATP-dependent DNase has been purified from Thermus thermophilus HB8 by a procedure involving streptomycin precipitation, DEAE-cellulose chromatography, Sephadex G-200 gel filtration and heparin-agarose affinity chromatography. ATP-dependent DNase activity was separated into two distinct peaks, Peak A and Peak B, by heparin-agarose affinity chromatography. Each peak fraction was further purified by ATP-agarose affinity chromatography. Peak A and Peak B were eluted from an ATP-agarose column at 0.14M and 0.28M KCl, respectively, each as a single peak. Both enzyme activities require ATP and Mg²⁺ for the degradation of double- and single-stranded DNAs, and degrade denatured DNA about 1.5 times faster than native DNA. The two peaks are optimally active at 69°C and have similar optimal pH ranges from 8.2 to 9.2. The two purified peaks were unstable on storage at -20°C, but were remarkably stabilized by addition of 0.4mg/ml bovine serum albumin. Ammonium sulfate strongly inhibits the activities of both peaks. The molecular weights of Peak A and Peak B are about 170, 000 as estimated by glycerol gradient sedimentation. The average chain lengths of denatured DNA produced by Peak A and Peak B were 4.2 and 3.6, respectively, and the products were terminated by 5'-phosphoryl and 3'-hydroxyl groups. The limit-digested products of denatured DNA produced by Peak B consist of mono-, di-, tri-, tetra-, and pentanucleotides along with some larger fragments. The mode of action of both activities is processive and Peak A does not attack double-stranded circular DNA.