Question

Which of the following statement is correct for DNA polymerase I of E. coli?
A. Also known as Kornberg polymerase
B. Possesses 5’exonuclease activity
C. Possesses 3’exonuclease activity
D. Plays central role in replication of its genome
Choose the correct answer from the options given below

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

Hint:

DNA Polymerase I (Kornberg polymerase) is unique because it is the only E. coli polymerase with "5' to 3' exonuclease" activity, which is essential for removing RNA primers. DNA Polymerase III is the primary replicative machine.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
DNA Polymerase I (Pol I) was the first DNA-synthesizing enzyme isolated from E. coli by Arthur Kornberg.
It is a multi-functional, single-polypeptide enzyme with both polymerizing and exonucleolytic activities.

Step 2: Detailed Explanation:
Let us evaluate each statement:
A is correct: DNA Polymerase I was discovered by Arthur Kornberg in 1956, for which he received the Nobel Prize, and is commonly referred to as the Kornberg polymerase.
B is correct: Unlike other DNA polymerases, Pol I possesses a unique 5' to 3' exonuclease activity in its small N-terminal domain.
This activity allows it to remove RNA primers from Okazaki fragments during replication (nick translation) and excise damaged DNA during repair.
C is correct: It also possesses a 3' to 5' exonuclease activity in its large C-terminal domain (Klenow fragment), which serves a proofreading function to excise mismatched nucleotides.
D is incorrect: Although highly abundant, Pol I is not the primary replicative enzyme.
Because of its slow polymerization rate and low processivity, its role is limited to primer removal and gap filling.
The central role in genome replication is carried out by DNA Polymerase III.
Therefore, only statements A, B, and C are correct.

Step 3: Final Answer:
Statements A, B, and C are correct, which corresponds to option (A).