**Executive Summary**
Researchers from the Bose Institute, Kolkata, published a study on April 2, 2026, revealing a fundamental flaw in the "universal $\sigma$-cycle" model of bacterial transcription. The study demonstrates that in *Mycobacterium tuberculosis*, certain proteins do not dissociate during transcription as previously believed, providing a new understanding of how the bacteria survive stress. This discovery establishes a foundation for developing innovative antimicrobial strategies to combat drug-resistant tuberculosis by targeting specific protein-protein interactions.
**Key Points / Main Content**
**Revision of Biological Models**
* The study overturns the long-standing "universal $\sigma$-cycle" theory taught in textbooks, which assumed $\sigma$ factors must be released from RNA polymerase to begin transcription elongation.
* Research indicates that bacteria do not rely on a single mechanism but use multiple, finely tuned strategies to regulate gene expression.
**Behavior of $\sigma$ Factors in M. Tuberculosis**
* **$\sigma$A and $\sigma$E:** The primary housekeeping $\sigma$ factor ($\sigma$A) and the stress-responsive factor ($\sigma$E) are released from RNA polymerase during elongation, either immediately or gradually.
* **$\sigma$F:** This factor, linked to stress survival and adaptation, remains stably associated with the enzyme throughout the transcription process.
* **Sustained Expression:** The retention of $\sigma$F suggests a previously unknown mechanism that ensures the bacterium can maintain the expression of stress-response genes.
**New Antimicrobial Strategy**
* The research identifies $\sigma$–RNA polymerase interactions as highly specific targets for drug development.
* Future therapies may focus on disrupting these critical protein-protein interactions rather than targeting enzyme active sites, where antibiotic resistance frequently emerges.
**Methodology and Validation**
* The team utilized advanced biochemical and cellular techniques, including in vitro transcription assays and fluorescence-based measurements.
* Findings were validated in vivo using chromatin immunoprecipitation followed by quantitative PCR.
**Impact Analysis**
**Scientific and Academic Community**
**Impact**
The discovery challenges decades of established molecular biology teaching regarding bacterial transcription. It provides a more accurate model of how *M. tuberculosis* regulates genes under extreme stress.
**Action Required**
Researchers and educators must update molecular biology frameworks and textbooks to reflect that the $\sigma$-cycle is not universal across all bacteria or regulatory proteins.
**Pharmaceutical Developers**
**Impact**
The study identifies new, specific targets for antimicrobial development that are less prone to traditional resistance mechanisms found at enzyme active sites.
**Action Required**
Drug development programs should explore the disruption of protein-protein interactions between $\sigma$ factors and RNA polymerase to create the next generation of TB therapies.
**Public Health Sector**
**Impact**
The findings offer a potential long-term solution to the global threat of drug-resistant tuberculosis by paving the way for more effective treatments.
**Action Required**
Stakeholders should support and fund further research into these specific bacterial targets to advance fundamental science into clinical applications.
Key Entities Referenced
Bose Institute, Kolkata: An autonomous institute of the Department of Science and Technology (DST) that conducted the research on bacterial transcription in tuberculosis.
Department of Science and Technology (DST): The government department overseeing the autonomous Bose Institute and supporting the research on antimicrobial development.
Dr Jayanta Mukhopadhyay and Dr N Hazra: The lead researchers who discovered that the universal σ-cycle mechanism does not apply to all bacteria, specifically Mycobacterium tuberculosis.
Nucleic Acids Research: The international peer-reviewed journal where the study uncovering the fundamental flaw in the bacterial gene expression model was published.
Ministry of Science & Technology
Altered understanding of bacterial transcription
mechanism can pave new path to combat
tuberculosis
Posted On: 02 APR 2026 3:31PM by PIB Delhi
A team of scientists has uncovered a fundamental flaw in a long-standing model of how bacteria control
gene expression that can form the base for innovative strategies to combat tuberculosis and other bacterial
infections.
Tuberculosis is one of the world’s deadliest infectious diseases, and drug-resistant strains pose an
increasing global threat to cure of the disease. M. tuberculosis (TB) bacteria survive inside the human host
by precisely regulating gene expression under extreme stress conditions.
For years, scientists believed that a protein called σ factor binds RNA polymerase, initiates bacterial
transcription and is then released once the enzyme begins elongating RNA. This process, known as the σ-
cycle, was assumed to be universal across bacteria, including TB bacteria.
A new study from Bose Institute, Kolkata, an autonomous institute of the Department of Science and
Technology (DST), overturns this assumption.
The Researchers Dr Jayanta Mukhopadhyay and Dr N Hazra found that while some σ factors in M.
tuberculosis dissociate from RNA polymerase during transcription, others remain firmly attached
throughout the process.
Their research, published in the international journal Nucleic Acids Research, reveals that a mechanism
taught for decades in molecular biology textbooks—the so-called “universal σ-cycle”, does not apply to
all bacteria or all regulatory proteins.
The study focuses on tuberculosis (TB) causing bacteria, Mycobacterium tuberculosis, and shows that
different σ (sigma) factors, proteins that guide RNA polymerase to specific genes, behave in strikingly
different ways during transcription, the first step of gene expression.
Fig: Differential Association of Different σ Factors with RNA Polymerase of Mycobacterium Tuberculosis
during Transcription ElongationUsing a combination of advanced biochemical and cellular techniques, the researchers examined three
distinct σ factors. These include σA, the primary housekeeping σ factor, σE, a stress-responsive σ factor
and σF linked to stress survival and adaptation.
They discovered that σA and σE are released from RNA polymerase during transcription elongation, either
immediately or gradually. In contrast, σF remains stably associated with the enzyme, even as transcription
proceeds. This study, published in the journal Nucleic Acids, shows that bacteria do not rely on a single
universal mechanism. They used multiple, finely tuned strategies to regulate gene expression.
The discovery that σF remains bound to RNA polymerase suggests a so far unknown mechanism by which
the bacterium ensures sustained expression of stress-response genes, an insight with important
implications for TB biology.
By showing that σ–RNA polymerase interactions vary depending on σ-factor architecture, the study
highlights new, highly specific targets for antimicrobial development. Instead of targeting enzyme active
sites—where resistance often emerges—future drugs could disrupt critical protein–protein interactions
essential for bacterial survival.
The team used in vitro transcription assays, fluorescence-based measurements, high-resolution protein
interaction studies and in vivo validation using chromatin immunoprecipitation, followed by quantitative
PCR. As antibiotic resistance continues to rise, insights like these, rooted in basic molecular understanding
can advance fundamental science and may prove crucial in shaping the next generation of antimicrobial
therapies.
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NKR/FT
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