6. A mutation in which one of the following sigma factors may be a possible cause for E. colt failing to adapt in response to thermal stress?
(1) σ⁷⁰        (2) σ³² 
(3) σ⁵⁴        (4) σ ⁴⁵

Correct Answer: (2) σ³²

Explanation:

Thermal Stress and Heat-Shock Response in E. coli

• When E. coli experiences elevated temperatures, it triggers a heat-shock response to prevent protein denaturation and misfolding.

• This response is mediated by heat-shock proteins (HSPs) such as DnaK, GroEL, GroES, HtpG, etc.

• The key regulatory factor in initiating the transcription of these genes is Sigma 32 (σ³²).

What Is Sigma 32 (σ³²)?

• Also known as RpoH, σ³² is the heat-shock sigma factor.

• It directs RNA polymerase to the promoters of heat-shock genes.

• Without functional σ³², E. coli cannot express chaperones or proteases needed for survival during heat stress.

Other Options Explained:

Correct Answer Recap: (2) σ³²

• Mutation in σ³² impairs heat-shock gene transcription, making E. coli vulnerable to thermal stress.

• It is critical for survival during sudden temperature increases.

CSIR NET Takeaways:

• Know the specific roles of sigma factors in bacterial stress responses.

• σ³² (RpoH) = Heat shock

• σ^S = Stationary phase/general stress

• σ⁷⁰ = Routine transcription

• σ⁵⁴ = Nitrogen metabolism

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