FIG. 3.

The exonuclease activities of the purified Xon⁺, XonA2, and SbcB15 proteins were measured at the indicated pH values of the reaction mixture (67 mM Tris-HCl, 0.67 mM MgCl₂, 10 mM β-mercaptoethanol) and at two temperatures (solid bars, 37°C; open bars, 30°C). Each assay mixture contained 0.15 U of Xon⁺, XonA2, or SbcB15 protein. Activities were expressed relative to those obtained for each enzyme at 37°C and pH 9.5 (100%). Data are means from experiments performed in duplicate. Error bars, deviations from the means.