(A) Reaction mixtures (20 µl) containing 50 mM Tris-HCl (pH 8.0), 1 pmol of 32P-labeled DNA substrate (gapped duplexes or simple primer-template as illustrated above the lanes), 100 µM each of dATP, dGTP, dCTP and dTTP (dNTPs), 1.25 mM CoCl2, and MsmPolD2 as indicated above the lanes were incubated for 10 min at 37°C. (B) Reaction mixtures (140 µl) containing 50 mM Tris-HCl (pH 8.0), 100 µM each of dATP, dGTP, dCTP and dTTP (dNTPs), 1.25 mM CoCl2,, 7 pmol of 32P-labeled substrate (simple primer-template or gapped duplex as illustrated below the lanes), and 1.2 µg of MsmPolD2 were incubated at 37°C. Aliquots (20 µl) were withdrawn at the times specified and quenched immediately with EDTA/formamide. The products were analyzed by PAGE and visualized by autoradiography.