Question

Which of the following function of the RNA Polymerase enzyme is affected when $\beta'$ subunit is mutated?

• A. Template binding
• B. RNA Chain inititation
• C. RNA chain elongation
• D. Promotor sequence identification

Hint:

To remember the subunit functions:
- $\beta$ = Catalytic center (elongation).
- $\beta'$ = Template DNA binding.
- $\sigma$ = Promoter recognition.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
In prokaryotes, the core RNA polymerase is a multi-subunit enzyme complex with the composition $\alpha_2\beta\beta'\omega$.
Each subunit has a highly conserved, specialized structural or functional role in transcription.
Detailed Explanation:
Let us analyze the specific roles of the different RNA polymerase subunits:
- $\alpha$ Subunits ($\alpha_2$): Essential for the assembly of the core enzyme and for binding to upstream promoter elements and regulatory transcription factors.
- $\beta$ Subunit: Houses the main catalytic center of the enzyme, facilitating phosphodiester bond formation during both RNA chain initiation and elongation.
- $\beta'$ Subunit: This is the largest subunit of the core enzyme.
It is primarily responsible for binding the DNA template strand and keeping the transcription bubble stable during the transcription process.
Therefore, a mutation in the $\beta'$ subunit directly impairs the enzyme's ability to bind to the DNA template.
- $\sigma$ Subunit (Sigma factor): When combined with the core enzyme to form the holoenzyme ($\alpha_2\beta\beta'\omega\sigma$), it is solely responsible for promoter sequence identification and initiation site specificity.
- $\omega$ Subunit: Aids in the assembly of the RNA polymerase complex.

Step 2: Final Answer:
A mutation in the $\beta'$ subunit of prokaryotic RNA polymerase primarily affects template binding, corresponding to option (A).