Competition experiments of the lead cleavage reaction with four different metal ions. Lead cleavage reactions were done in buffer containing 2 mM Mg²⁺ and 5 mM Pb²⁺ with increasing amounts of either Mg²⁺, Mn²⁺, Ca²⁺ or Zn²⁺. (A) Primer extension analysis of the three strong Pb²⁺ cleavage sites are shown and the positions of the nucleotides are indicated with an arrow. (B) Quantitative PhosphorImager analysis of the competition experiments.