In bacterial DNA replication, which DNA polymerase has 3′→5′ exonuclease proofreading activity?

• A. Primase (DnaG)
• B. DNA polymerase II
• C. DNA polymerase III
• D. DNA polymerase I

Answer: (C)

Verified step by step guidance

1. Understand that DNA polymerases are enzymes responsible for synthesizing DNA strands during replication, and some have proofreading abilities to ensure accuracy.
2. Recall that 3′→5′ exonuclease activity refers to the enzyme's ability to remove nucleotides from the end of a DNA strand in the reverse direction, which is essential for proofreading and correcting errors.
3. Identify the roles of the given enzymes: Primase (DnaG) synthesizes RNA primers and does not have proofreading activity; DNA polymerase I is involved in removing RNA primers and filling gaps but has limited proofreading; DNA polymerase II has some repair functions and proofreading activity but is not the main replicative polymerase.
4. Recognize that DNA polymerase III is the primary enzyme responsible for the bulk of DNA synthesis during bacterial replication and possesses strong 3′→5′ exonuclease proofreading activity to ensure high fidelity.
5. Conclude that among the options, DNA polymerase III is the enzyme with 3′→5′ exonuclease proofreading activity during bacterial DNA replication.