Figure 2.

RNA–DNA hybridization at the –10th position restricts translocation by a conserved, lid domain-dependent mechanism. Translocation inhibitor Nun stimulates pyrophosphorolysis by TEC U10 (A) and inhibits pyrophosphorolysis in a major fraction of TEC U9 (B). The TECs were pre-incubated with 1 μM Nun or the same volume of Nun storage buffer in the absence of Mg²⁺, and pyrophosphorolysis time courses were analyzed in the presence of 2.5 mM PPi and 5 mM MgCl₂. The data points were fitted with a single exponential function. The translocation schematic at right in (A) and (B) show the pre-translocated fraction of TEC U10 and TEC U9 inferenced from the TEC U10 pyrophosphorolysis rate in the presence of Nun. The detailed description of the translocation schemes is in the text. (C) Pyrophosphorolysis rate constants at 2.5 mM PPi and 5 mM MgCl₂ in TECs U9 and U10 formed by the WT RNAP, Δlid RNAP and yeast Pol II.