Authors: Nelly Said, Tarek Hilal, Nicholas D. Sunday, Ajay Khatri, Jörg Bürger, Thorsten Mielke, Georgiy A. Belogurov, Bernhard Loll, Ranjan Sen, Irina Artsimovitch, Markus C. Wahl
Summary: Factor-dependent transcription termination mechanisms are poorly understood. We determined a series of cryo-electron microscopy structures portraying the hexameric ATPase ρ on path to terminating NusA/NusG-modified elongation complexes. An open ρ ring contacts NusA, NusG, and multiple regions of RNA polymerase, trapping and locally unwinding proximal upstream DNA. NusA wedges into the ρ ring, initially sequestering RNA. Upon deflection of distal upstream DNA over the RNA polymerase Zinc-binding domain, NusA rotates underneath one capping ρ subunit, which subsequently captures RNA. Following detachment of NusG and clamp opening, RNA polymerase loses its grip on the RNA:DNA hybrid and is inactivated. Our structural and functional analyses suggest that ρ and other termination factors across life may utilize analogous strategies to allosterically trap transcription complexes in a moribund state.
Source: Science, 2020; eabd1673