Largest subunit (beta') of Bacterial DNA-dependent RNA polymerase (RNAP), C-terminal domain
Bacterial RNA polymerase (RNAP) is a large multi-subunit complex responsible for the synthesis of all RNAs in the cell. This family also includes the eukaryotic plastid-encoded RNAP beta" subunit. Structure studies suggest that RNAP complexes from different organisms share a crab-claw-shape structure with two pincers defining a central cleft. Beta' and beta, the largest and the second largest subunits of bacterial RNAP, each makes up one pincer and part of the base of the cleft. The C-terminal domain includes a G loop that forms part of the floor of the downstream DNA-binding cavity. The position of the G loop may determine the switch of the bridge helix between flipped-out and normal alpha-helical conformations.