Figure 4. Architecture and Pol III-specific function of the C53/C37 heterodimer and C11.

a, Model of the Pol III C53/C37 heterodimer shown in ribbon representation bound to the Pol III core (left), Pol II homologue TFIIFα/β bound to the Pol II core (center, PDB 4v1n) and Pol I homologue A49/A34.5 bound to the Pol I core (right, PDB 4c3i). The red asterisk (left panel) marks the position of the five residues that upon deletion lead to a terminator read-through phenotype¹³. Schematic representations of C53 and C37 show the domain boundaries of the dimerization domain (DD) and additional elements. Dotted lines indicate unstructured regions. b, Conformation of subunit C11 in Pol III (left), subunit Rpb9 in Pol II (middle), and subunit A12.2 in Pol I. Subunits C11, Rpb9 and A12.2 are depicted with yellow surface rendering; C53/C37, TFIIFα/β and A49/A34.5 are depicted in ribbon representation, all other subunits are colored in grey. Arrows indicate the potential movement of the C11 C-terminal TFIIS domain, the red dotted circle indicates the linker that connects the C11 N- and C-terminal domains.