Indian Scientists Challenge Bacterial Gene Regulation Model

In March 2026, researchers from the Bose Institute published a study in Proceedings of the National Academy of Sciences (PNAS) overturning the long-accepted “sigma (σ) cycle” model of bacterial gene regulation.

Key Points

Breakthrough In Bacterial Biology: The study challenges the five-decade-old sigma cycle model that explains how bacteria switch genes on and off during transcription.
Textbook Model Questioned: Traditional understanding, based largely on Escherichia coli and its σ70 factor, held that sigma factors detach from RNA polymerase after initiating transcription.
New Discovery in Bacillus subtilis: Researchers found that the principal sigma factor σA in Bacillus subtilis remains attached to RNA polymerase throughout the transcription process.
Modified E. coli Variant: A modified σ70 factor (lacking segment 1.1) in E. coli was also found to remain stably bound, unlike the full-length σ70 which detaches stochastically.
Advanced Research Techniques Used: The team employed biochemical assays, chromatin immunoprecipitation and fluorescence-based imaging to observe sigma factor behaviour in real time.
Not A Universal Mechanism: Findings demonstrate that the sigma cycle does not apply universally across bacterial species, fundamentally reshaping understanding of gene regulation.