Incorrect incorporation into Sym/Sub U. (A) Apparent inhibition by high NTP concentrations. Products formed in the presence of 3000 (circles), 5000 (squares) and 6000 (triangles) μM GTP were quantified and plotted as a function of time in seconds. All products were included in the calculations for this graph. These data did not fit a single exponential: the line is provided only for improved viewing. (B) Apparent multiple turnovers with incorrect base. Quantified products (all) formed in the presence of 375 (circles), 700 (squares), 1500 (triangles) and 3000 (diamonds) μM UTP and plotted as a function of time in seconds. These data did not fit a single exponential: the line is provided only for improved viewing. (C) Formation of higher molecular weight products in the presence of incorrect, but not, correct NTP. Left five lanes: 1 μM Sym/Sub U incubated with 500 μM ATP (correct base) for the indicated times (in minutes). Right five lanes: 1 μM SSU incubated with 1500 μM UTP (incorrect base) for indicated time (minutes). Samples were denatured and electrophoresed in a 20% denaturing PAGE. Size of RNA species is indicated at the right of the gel. 10 mer is the starting material.