(a) The substrates used are the same as in Figure 1, except that the RNA donor is 5′-radiolabeled, not the DNA primer. (b) Intact donor RNA (D) and primary (1) or secondary (2) cleavage products are generated over time (1, 5, 15 30 min) in the absence (−NC) and presence (+NC) of NC. RNA cleavage products were visualized in denaturing polyacrylamide gel electrophoresis. Gel lanes are numbered 1–20. Lanes 1 - 5 WT RT, 5 - 8 E478Q RT, 9 - 12 H539F RT, 13 - 16 H539D RT, 17 - 20 H539R RT.