5. In bacteria, heat-shock response is primarily controlled by
(1) Sigma S (σs) (2) Sigma 32 (σ32)
(3) ma E (σE) (4) Sigma 70 (σ70)

MCQ: In Bacteria, the Heat-Shock Response Is Primarily Controlled By:

1. Sigma S (σⁿ or σ^S)

2. Sigma 32 (σ³²)

3. Sigma E (σ^E or σ^24)

4. Sigma 70 (σ⁷⁰)

Correct Answer: (2) Sigma 32 (σ³²)

Explanation:

The heat-shock response in bacteria, especially Escherichia coli, is a protective transcriptional response triggered by sudden increases in temperature. It helps the cell survive proteotoxic stress by expressing chaperones and proteases.

What Is Sigma 32 (σ³²)?

• Sigma 32 is also known as RpoH.

• It is an alternative sigma factor that guides RNA polymerase to heat-shock gene promoters.

• Genes under σ³² control include dnaK, groEL, groES, htpG, and others involved in protein folding and degradation.

Role of Other Sigma Factors:

Key Concept for CSIR NET Life Science:

• Heat-shock proteins (HSPs) are molecular chaperones.

• Their transcription is activated by σ³² in response to high temperatures.

• mRNA for σ³² is always present, but translation and stability of σ³² protein increase after heat shock.

CSIR NET Takeaways:

• Memorize major sigma factors and their roles in bacterial stress responses.

• Be able to distinguish between σ³² (heat shock), σ⁷⁰ (housekeeping), and σ^E (envelope stress).

• Understand that alternative sigma factors reprogram RNA polymerase specificity.

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