Single-molecule experiments reveal NusG displaces transcription initiation factor σ70 from mature elongation complexes.

ABSTRACT: The Escherichia coli transcription initiation factor σ70 was long believed to dissociate from RNA polymerase after promoter escape, following synthesis of short ~9-11 nt RNAs. However, recent evidence indicates σ70 is retained in elongation complexes (ECs), where it enhances pausing-implying that stochastic or factor-mediated displacement is required for processive elongation. Using fluorescence correlation spectroscopy, we quantified σ70 retention in the presence of elongation factors NusG and NusA, demonstrating that NusG-but not NusA-actively promotes σ70 dissociation. Single-molecule TIRF further revealed that NusG-mediated σ70 dissociation becomes favourable as ECs progress, with lower energy barriers for displacement in later elongation stages. These findings suggest a broader mechan

SUBMITTER: Mukherjee P 

PROVIDER: S-EPMC12802917 | biostudies-literature | 2026 Jan

REPOSITORIES: biostudies-literature