Figure 4.

Ionic accessibility of polymerase and exonuclease active sites of PabPolB. (A) Primer-template used for 3′-exonuclease primer degradation and primer extension experiments, in panels B and C and D and E, respectively. It consists of a Cy5-labeled 17-mer primer annealed to a DNA template of 87-nt in length. Ion displacement experiment is carried out at fixed Mg²⁺ and Ca²⁺ concentrations and by increasing metal ion competitor concentrations, respectively, in panels B–D and C–E. PabPolB is pre-incubated at the indicated fixed metal concentrations. Chased experiment is initiated by co-addition of p/t (17/87) and increased ion competitor concentrations. Equimolar concentrations are shown framed. Reference oligodeoxynucleotides of 87, 17 and 8 bases are indicated on the right of each panel.