ATP-dependent excision of chain-terminating nucleotides with WT and mutant RTs. The primers were initially chain terminated with TFV-DP (A) or ZDV-MP (B). Combined excision/rescue reactions were compared in time course experiments. Reactions were stopped at the indicated time points and samples were analyzed in denaturing 6% polyacrylamide gels. Graphic representations of efficiency of rescued DNA synthesis from gel-based assays are shown on the left below the gel graph. Calculated excision rate constants (k) (×10-3 s-1) ± SD (P ≤ 0.01, compared to WT; two-tailed Student's t-test) are shown on the right.