Question

The sigma \((\sigma)\) subunit of prokaryotic RNA polymerase A. is part of the core enzyme. B. binds the antibiotic rifampicin. C. is inhibited by \(\alpha\) -amanitin. D. must be present for transcription to occur. E. specifically recognizes promoter sites.

Short answer

A. It is part of the core enzyme. B. Rifampicin binds to it and inhibits its function. C. α-amanitin is an inhibitor of its activity. D. It must be present for transcription to occur. E. Its specificity is determined only by its amino acid sequence. Answer: D. It must be present for transcription to occur.

Step-by-step solution

Understand RNA Polymerase

RNA polymerase is the enzyme responsible for synthesizing RNA from a DNA template; in prokaryotes, it consists of a core enzyme and a sigma factor. The core enzyme is responsible for RNA synthesis, whereas the sigma factor helps in recognizing promoter sequences on the DNA.

Define the Role of Sigma Subunit

The sigma subunit of prokaryotic RNA polymerase is a separate protein that associates with the core enzyme. It helps the RNA polymerase enzyme recognize specific promoter sites on the DNA and initiate transcription.

Compare Sigma Subunit Properties to Options

A. The sigma subunit is not part of the core enzyme but instead binds to it for promoter recognition. B. Rifampicin binds to the core RNA polymerase enzyme, not the sigma subunit. C. \(\alpha\)-amanitin is an inhibitor of eukaryotic RNA polymerase, not prokaryotic RNA polymerase. D. The sigma subunit is necessary for transcription initiation as it recognizes promoter sequences on DNA. This statement is correct. E. While the sigma subunit is indeed responsible for promoter recognition, its specificity is influenced by the promoter sequences and additional transcription factors.

Conclusion

Among the options provided, option D (the sigma subunit must be present for transcription to occur) is the correct property regarding the sigma subunit of prokaryotic RNA polymerase.