Transcription termination factor {rho} polymerizes under stress

Bacterial RNA helicase {rho} is a genome sentinel that terminates synthesis of damaged and junk RNAs that are not translated by the ribosome. Co-transcriptional RNA surveillance by {rho} is essential for quality control of the transcriptome during optimal growth. However, it is unclear how bacteria protect their RNAs from overzealous {rho} during dormancy or stress, conditions common in natural habitats. Here we used cryogenic electron microscopy, biochemical, and genetic approaches to show that residue substitutions, ADP, or ppGpp promote hyper-oligomerization of Escherichia coli {rho}. Our results demonstrate that nucleotides bound at subunit interfaces control {rho} switching from active hexamers to inactive higher-order oligomers and extended filaments. Polymers formed upon exposure to antibiotics or ppGpp disassemble when stress is relieved, thereby directly linking termination activity to cellular physiology. Inactivation of {rho} through hyper-oligomerization is a regulatory strategy shared by RNA polymerases, ribosomes, and metabolic enzymes across all life.