Fig. 1. X-ray crystal structure of TelSi3ΔN.

(A) The thick bars represent the primary sequences of the largest subunits of the bacterial, chloroplast and archaeal RNAPs. Domains (Si3, green boxes) and structural motifs (RH, rim helix; BH, bridge helix; TL, trigger loop) are labeled. The lettered boxes represent evolutionarily conserved regions. The split ends of the two polypeptides are indicated by black triangles. (B) Crystals of TelSi3ΔN. (C) Structure of TelSi3ΔN. Six molecules of TelSi3ΔN (I~VI) are present in the asymmetric unit. Molecules are depicted as cartoon models with transparent surfaces, and each molecule is denoted by a unique color and labeled. (D) The backbone is colored as a ramp from the N-terminus to the C-terminus, from blue/cyan/green/yellow/orange/red. SBHMs are labeled 1 to 8, and subdomains (tail, fin, body and head) are indicated. The TelSi3ΔN structure lacks SBHM-1, and the trigger loops (TL_N and TL_C) are depicted as blue oval and pink cylinders, respectively, with black lines showing their connections with TelSi3ΔN. (E) Molecules 1 and 3 of TelSi3ΔN are superimposed via fin subdomains, revealing flexibility in the orientation between the fin and body/head subdomains.