Abstract
DNA-dependent RNA polymerase (RNAP) synthesizes RNA complementary to the template DNA. During transcript elongation, RNAP often undergoes backward translocation ('backtracking') by dissociating the 3' end of the nascent RNA transcript from the template DNA. While the backtracked state of RNAP is inactive in RNA elongation, it actively hydrolyses the RNA 3' end to regenerate the active elongation complex. To study the structural basis of the backtracked state and its cleavage activity, two backtracked RNAP complexes were reconstituted by assembling Thermus thermophilus RNAP with designed nucleic acid scaffolds. The reconstituted backtracked complexes were active in the transcript-cleavage reaction. These complexes were crystallized and X-ray diffraction data sets were obtained at resolutions of 3.4 and 3.7 Å.