Molecular mechanisms of substrate-controlled ring dynamics and sub-stepping in a nucleic-acid dependent hexameric motor

Ring-shaped hexameric helicases and translocases support essential DNA, RNA, and protein-dependent transactions in all cells and many viruses. How such systems coordinate ATPase activity between multiple subunits to power conformational changes that drive the engagement and movement of client substrates is a fundamental question. Using the E. coli Rho transcription termination factor as a model system, we have employed solution and crystallographic structural methods to delineate the range of conformational changes that accompany distinct substrate and nucleotide cofactor binding events. SAXS data show that Rho preferentially adopts an open-ring state in solution, and that RNA and ATP are bo