Fig. 3: Human Pol I stalk is made out of only one subunit.

a, Domain composition of the human RPA43 (top) and its yeast A43 homologs: S. cerevisiae (middle; PDB 5M64)²⁵ and S. pombe (bottom; PDB 7AOE)⁴³. The colored bar indicates the region modeled in the structures denoted as ‘built’. Rpb7, Rpb7-like domain; OB, oligonucleotide/oligosaccharide binding domain. b, Structure overlay of the human RPA43 subunit with its yeast (S. cerevisiae) homolog (PDB: 5M64)²⁵. c–j, Yeast Pol I stalk (PDB: 5M64)²⁵ (c,e,g,i) compared with human Pol I stalk (d,f,h,j). Stalk subunits A43 (yeast) and RPA43 (human) (blue) and yeast A14 (pink) are shown in the cartoon representation, while the rest of the Pol I is shown in the surface representation, colored as in Fig. 1. The rotations of the views between the panels are indicated in the top right corner of the panels. c,d, Cryo-EM density corresponding to A43/RPA43 (gray) and A14 (pink) is shown in a transparent representation. e,f, Structurally homologous N-terminal portions of the A43 and RPA43 subunits are circled. g,h, The yeast A190 loop (562–573) structure (g) is overlaid on the human structure (h) as a transparent cartoon. h, In humans, the RPA1 loop (527–533) (cartoon representation, solid) is less structured and folds away from the stalk (bottom black arrow). The lower part of the stalk in humans tilts in the same direction (black arrows) when compared with yeast (overlaid transparent cartoon of the lower part of the yeast stalk). e–h, Outlines of the yeast specific extensions in A135 and ACB23 marked in e and g are overlaid onto the human structure in f and h, respectively. i,j, The human Pol I stalk leans (purple arrow) toward the RPA49 tWH domain when compared with the yeast structure, which is overlaid as a transparent cartoon.