How to stop RNA polymerase Timely and tunable cessation of RNA synthesis is vital for cellular homeostasis. RNA helicases such as the archetypal termination factor r actively dismantle transcription complexes, but the transitory nature of termination makes the process hard to study structurally. Said et al. assembled ρ-bound transcription complexes and studied them using cryo–electron microscopy with an approach that captured a series of functional states en route to termination. They found an extensive and dynamic network of r interactions with RNA polymerase, nucleic acids, and accessory Nus factors. ρ mediates stepwise rearrangements of these contacts, transforming an actively transcribing complex into a moribund pretermination intermediate. Science , this issue p. 44