Question

The constituent units of a core E.coli DNA polymerase III are
(A). \(\alpha\) (alpha) subunit
(B). \(\epsilon\) (epsilon) subunit
(C). \(\theta\) (theta) subunit
(D). \(\delta\) (delta) subunit
Choose the correct answer from the options given below:

• A. (A) and (B) only.
• B. (A) and (C) only.
• C. (B), (C) and (D) only.
• D. (A), (B) and (C) only.

Hint:

Remember the core of DNA Polymerase III as \(\alpha\epsilon\theta\):
- \(\alpha\): The builder (polymerase).
- \(\epsilon\): The editor (proofreader).
- \(\theta\): The assistant (enhances proofreading).

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
DNA Polymerase III is the primary enzyme complex responsible for synthesizing the leading and lagging strands during DNA replication in E. coli.

Step 2: Detailed Explanation:
1. The complete DNA Polymerase III holoenzyme is a multi-subunit complex.
2. The catalytic core of this holoenzyme consists of three distinct subunits:
- \(\alpha\) (alpha) subunit (A): Encoded by the dnaE gene, it contains the 5'\(\rightarrow\)3' DNA polymerase activity.
- \(\epsilon\) (epsilon) subunit (B): Encoded by the dnaQ gene, it contains the 3'\(\rightarrow\)5' proofreading exonuclease activity.
- \(\theta\) (theta) subunit (C): Encoded by the holE gene, it binds to and stimulates the proofreading activity of the \(\epsilon\) subunit.
3. The \(\delta\) (delta) subunit is part of the clamp loader complex, not the catalytic core.
4. Therefore, the core units are \(\alpha\), \(\epsilon\), and \(\theta\).

Step 3: Final Answer:
The constituent units of the core enzyme are (A), (B), and (C) only.