New Research on “sigma (σ) cycle” Model

Indian scientists have played a key role in overturning a nearly five-decade-old model explaining how bacteria regulate gene expression, challenging long-standing textbook concepts in molecular biology.

A new study led by researchers from the Bose Institute, an autonomous institute under the Department of Science and Technology (DST), in collaboration with Rutgers University, has questioned the widely accepted “sigma (σ) cycle” model of bacterial gene regulation.

The findings were published in the prestigious journal Proceedings of the National Academy of Sciences (PNAS).

What Was the Sigma (σ) Cycle Model?

For nearly 50 years, biology textbooks have described the sigma (σ) cycle as a universal mechanism by which bacteria initiate gene transcription. According to this model:

• Sigma (σ) factors bind to RNA polymerase to initiate transcription.
• After initiation, the sigma factor detaches.
• RNA polymerase then continues elongating the RNA strand independently.

This concept was largely based on studies of the bacterial strain Escherichia coli and its σ70 factor, and was believed to apply broadly across bacterial species.

What the New Study Found

The new research demonstrates that this mechanism is not universal.

In the bacterium Bacillus subtilis, the principal transcription initiation factor, σA, was found to remain bound to RNA polymerase throughout the transcription process, rather than detaching after initiation.

Additionally, a modified version of the σ70 factor in E. coli was also observed to stay attached during transcription, further challenging the traditional sigma cycle model.

Scientific Significance

The study reshapes fundamental understanding of bacterial gene regulation and suggests that transcription mechanisms may vary significantly across species.

By overturning a long-standing model, the findings:

• Highlight the importance of re-evaluating established biological concepts
• Open new avenues for research in microbiology and molecular genetics
• May influence future strategies in antibiotic development and synthetic biology

Source: DD