Fig. 3: Formation of UBP induces closure of trigger loop in E. coli RNAP elongation complex.

a−c Residues interacting with bound nucleotide triphosphate substrate are highlighted. Trigger loop (TL) and Bridge helix (BH) are colored in purple and green, respectively. Magnesium ion in black. Bottom column shows densities of TLs for (dB:STP), (dB:UTP) and (dS:BTP), respectively. R678 and R1106 belongs to β subunit of RNAP. R425, M932, F935 and H936 belongs to β′ subunit of RNAP.