Fig. 2: RNGTT docks in close proximity to the Pol II stalk and catalyzes 5′-triphosphate RNAs in different lengths.

a Ribbon model of RNGTT docks on the PEC cryo-EM map. TPase and GTase domains of RNGTT are represented as ribbons in orange and sea green, respectively, while other components as density maps with labels in corresponding colors. b Close-up view of TPase and GTase domains of RNGTT. The active centers are displayed as spheres and colored by elements. c OB fold of GTase interacts with Pol II stalk (cornflower blue) and RPB1 subunit (medium slate blue). Pol II is illustrated as grey density map. OB loop of OB-fold is highlighted in lime. d TPase domain lies at the RNA exit tunnel. The active center of TPase is displayed as spheres and colored by elements. The triphosphate of RNA is displayed as sticks. Oxygen is colored in red and phosphorus is in orange. e-f Comparison of PEC-RNGTT (e) and PEC (f) in the same view. (Pol II, grey; DSIF, wheat; KOWx-KOW4 domain, magenta). The blue ellipse circled the clash position between KOWx-KOW4 and RNGTT. g RNA in Pol II active center. Cryo-EM density of RNA is shown in semi-transparent red with its model fitted. Other components are showed as ribbons with labels in corresponding colors around. h In vitro guanylylation assay in the context of phosphorylated Pol II-DSIF-RNGTT complex. RNAs shorter than 23 nt correspond to the first ladder, while the others correspond to the second ladder. Bands of guanylylated RNAs are pointed out with arrows. The experiment was repeated at least three times. Source data are provided as a Source Data file.