Single-cell Analysis of Attenuation-Driven Transcription Reveals New Principles of Bacterial Gene Regulation

Transcription attenuation fine-tunes biosynthetic gene expression in bacteria via premature termination upon metabolic signals. In transcription initiation-controlled bacterial systems, promoter architecture and transcription factor binding sets the size of transcriptional bursts at σ ⁷⁰ promoters, while distal enhancer elements and associated transcriptional activators modulate burst frequency at σ ⁵⁴ promoters. Using the tryptophan biosynthesis operon as a model, we show that transcription attenuation, acting post-initiation and alongside transcriptional repression, simultaneously modulates both burst size and frequency from a σ ⁷⁰ promoter. This challenges the view that frequency modulation requires distal enhancer input and reveals that post-initiation mechanisms can shape divergent transcriptional bursting. We also uncover that bacteria use cross-feeding as a previously unrecognised strategy for controlling cell-to-cell variation in gene expression, with implications for metabolic coordination among cells. These findings redefine transcription dynamics within cell populations and suggest new principles by which bacteria regulate gene expression to adapt to environmental change.