Extended Data Fig. 8: Density corresponding to the DNA mimicking loop in the Pol I-RRN3 map.

a, Cartoon domain representation of the RPA1 subunit. The C terminus harboring the jaw extension termed ‘DNA-mimicking loop’ is shown on the close-up view. b, Overview representation of the Pol I-RRN3 structure. c, Close-up view of the additional density in the DNA binding cleft (left panel), which is then overlaid on the Pol I EC structure (middle panel), where it would overlap with the DNA backbone. Density seen in the cleft of human Pol I (left panel) overlaps with the yeast DNA mimicking loop (PDB: 4C3J¹⁹) (right panel). d, Close-up view of the first 10-residues of the DNA mimicking loop (stick representation) which bind to the RPA2 core (left panel). When the cryo-EM density corresponding to those residues is superimposed on the Pol I EC (middle panel) it overlaps with the turn from the HTH motif of subunit RPA49 (purple). The path of the first residues of the DNA mimicking loop is the same in yeast Pol I (right panel). b–d, Additional density lining the DNA binding cleft in the Pol I-RRN3 structure which likely corresponds to the DNA-mimicking loop is shown as transparent, blue surface. e, Sequence alignment of the human and yeast DNA mimicking loop. Dark blue marks identical residues and light blue similar residues. Dots mark gaps in the sequence.