Fig. 3.

(A) Detailed view of the interactions established between Asp¹²¹ and ssDNA ligands of the exonuclease active site. Residues involved in the interaction are shown as sticks. An ssDNA fragment is shown as a light-orange cartoon inside a transparent surface representation. (B) Hydrolysis of pNP-TMP. The assay was performed as described in Materials and Methods. Catalytic efficiency for the hydrolysis of pNP-TMP catalyzed by the wild-type (wt) ϕ29 DNAP (■) and mutants D121E (○), D121A (●), and D121N (□) was determined spectrophotometrically by monitoring p-nitrophenol production at 420 nm at 25 °C at the indicated times.