Extracellular nuclease from a thermophile, Streptomyces thermonitrificans: purification and characterization of the deoxyribonuclease activity

An extracellular nuclease from Streptomyces thermonitrificans (designated as nuclease Stn α) was purified to homogeneity with an overall yield of 2.8%. The M r of the purified enzyme was 39.6 kDa. The purified enzyme showed an exclusive requirement of Mn 2+ for its activity but is not a metalloprotein. The optimum pH for ds- and ssDNA hydrolysis were 7.0 and 7.5 whereas, the optimum temperature was 40 and 45 °C, respectively. The enzyme was inhibited by divalent cations, inorganic phosphate and pyrophosphate but not by 3′ and 5′ mononucleotides. Nuclease Stn α is a multifunctional enzyme and its substrate specificity is in the order of dsDNA > ssDNA ≫ RNA. The end products of both ds- and ssDNA hydrolysis were predominantly oligonucleotides (80–85%) and a small amount of 3′ mononucleotides (10–15%) suggesting an endo mode of action.