Figure 1.

Metal ion specificity of gp2 nuclease. (A) Effect of divalent cations on gp2 circular dsDNA nuclease activity. Supercoiled pBT115 DNA was incubated with purified gp2 alone or with gp2 in the presence of 10 mM Mg²⁺, Ca²⁺, Mn²⁺, Co²⁺, Zn²⁺ or Ni²⁺. After 1 h at 37°C, the reactions were stopped and DNA analyzed as described under ‘Materials and Methods’ section. R, relaxed circular; L, linear; CCC, covalently closed circular DNA. (B) Effect of divalent cations on gp2 linear dsDNA nuclease activity. Linear plasmid pBT115 (PstI-cleaved) was incubated with gp2 with or without different divalent cations and analyzed as above. (C) Dose-dependent effect of Mn²⁺ on gp2 nuclease activity. Supercoiled pBT115 DNA was incubated with gp2 in the presence of increasing concentrations of Mn²⁺. (D) Nuclease activity of gp2 with long linear DNA substrates in the presence of different Mn²⁺ concentrations. SPP1 (45 kb) or T5 (125 kb) phage DNAs were incubated with gp2 in the presence of increasing concentrations of Mn²⁺.