Fig. 2.

Structure of a Trf4p/Air2p subcomplex at 2.7-Å resolution. (A) Schematic of Trf4p and Air2p, indicating regions included in the crystallization construct. Air2p zinc knuckles are boxed. (B) Ribbons diagram with the catalytic and central domains of Trf4p in cyan and blue, respectively. Orange dots indicate positions of the aspartate residues in the catalytic triad. The fourth and fifth zinc knuckles of Air2p and adjacent linker regions (ZK4, ZK5) are yellow and green, respectively, and zincs are red. (C) Superposition of the Trf4p/Air2p subcomplex (blue/yellow and green) with another noncanonical RNA polymerase, CCA-adding enzyme from A. fulgidus (PDB ID 2DRA, cyan). The catalytic and central domains were superimposed separately because their relative orientation differs in the two structures.