Figure 4.

Pyrophosphorolytic activity of Dpo4. Comparison of polymerization and pyrophosphorolytic activities of Dpo4 with correctly paired (A) or mispaired (B) primer–template termini. Effect of increasing PPi concentrations on primer extension and degradation was studied in the absence of added dNTP (panel I), in the presence of the next correct dATP (panel II) or in the presence of incorrect dGTP nucleotide (panel III). The local template sequence is shown to the left of the gel. PPi-dependent inhibition of primer elongation (panel IV) or primer degradation (panel V) in reactions shown in panels I, II and III was calculated as percent of total primer termini. Open triangles (▵) represent the presence of dATP, open diamonds (◊) the presence of dGTP and open circles (○) the absence of dNTP.