Steps toward translocation-independent RNA polymerase inactivation by terminator ATPase ρ
Nelly Said, Tarek Hilal, Nicholas D. Sunday, Ajay Khatri, Jörg Bürger, Thorsten Mielke, Georgiy A. Belogurov, Bernhard Loll, Ranjan Sen, Irina Artsimovitch, M.C. Wahl
Abstract
Factor-dependent transcription termination mechanisms are poorly understood. We determined a series of cryo-electron microscopy structures portraying the hexameric adenosine triphosphatase (ATPase) ρ on a pathway 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. After 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 use analogous strategies to allosterically trap transcription complexes in a moribund state.