SDS – PAGE nuclease assay and biochemical analysis of Prevotella intermedia crude nuclease. (A) Pr. intermedia crude nuclease was detected in SDS – PAGE gels containing 0.2 mg ml −1 salmon sperm DNA . After electrophoresis, proteins were renatured. This was followed by incubation in activation buffer containing 1 m m MgCl 2 and 1 m m CaCl 2 for 3 h at 37°C. To visualize DNA degradation, gels were stained with ethidium bromide and examined under ultraviolet light. Two protein bands were observed to possess nuclease activity. (B) λ DNA was incubated with Pr. intermedia crude nuclease with or without 1 m m MgCl 2 and 1 m m CaCl 2 at 37°C for 10 min. Following electrophoresis, DNA was stained with ethidium bromide and visualized under ultraviolet light.