Fig. 3. The catalytic center of Pol I in the post- and pre-translocation states.

a Cryo-EM map and structural model of the DNA–RNA hybrid in the Pol I EC^post. Critical residues involved in catalysis are shown in sticks. The magnesium cation in the metal A position is shown in pink ball. b Close-up view of the catalytic center of Pol I EC^pre. The cryo-EM map is shown in mesh and critical residues are shown in sticks. c Conformational differences of hPol I (marine) and yPol I (gray) around the transcription fork. The yellow dash line indicates the putative path of the nontemplate strand.