Figure 4

Effects of addition of various monovalent and divalent salts on the double strand DNA activities of SXT-Exo, as determined by quenched PicoGreen assays. Panel A: Inhibition of the dsDNA exonuclease activities of SXT-Exo with sodium chloride (black squares), sodium phosphate (buffered to pH7.4; red circles) and sodium sulfate (blue triangles). SXT-Exo (2 pmol of trimers), PstI-linearized pUC18 (5 ng, 0.003 pmol) in Tris-HCl (25 mM, pH7.4), 0.5 mM MnCl₂; as well as the salt indicated in the figure (NaCl, Na₂HPO₄ (pH7.4), or Na₂SO₄; 0-500 mM); were incubated at 37°C for 30 mins. Panel B: Inhibition of the dsDNA exonuclease activities of SXT-Exo with potassium chloride (black squares), calcium chloride (red squares) and potassium sulfate (blue triangles). SXT-Exo (2 pmol of trimers), PstI-linearized pUC18 (5 ng, 0.003 pmol) in Tris-HCl (25 mM, pH7.4), 0.5 mM MnCl₂; as well as the salt indicated in the figure (KCl, CaCl₂ or K₂SO₄; 0-500 mM); were incubated at 37°C for 30 mins. Relative dsDNA exonuclease activities were calculated (as a percentage) by comparison with results from analogous assays that contained: SXT-Exo (2 pmol of trimers), PstI-linearized pUC18 (5 ng, 0.003 pmol) in Tris-HCl (25 mM, pH7.4), 0.5 mM MnCl₂, 50 mM NaCl. Graphs show the the mean values ± standard deviation. See methods for detailed experimental procedures.