In prokaryotic DNA replication, which DNA polymerase is primarily responsible for proofreading newly synthesized DNA via a $3\prime \to 5\prime$ exonuclease activity?

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

Answer: (B)

Verified step by step guidance

1. Understand the role of different DNA polymerases in prokaryotic DNA replication. DNA polymerase I, II, and III each have distinct functions during replication and repair.
2. Recall that proofreading during DNA replication involves the removal of incorrectly paired nucleotides by exonuclease activity in the 3\' to 5\' direction, which helps maintain replication fidelity.
3. Identify which DNA polymerase has the primary 3\' to 5\' exonuclease activity responsible for proofreading the newly synthesized DNA strand during replication.
4. Note that DNA polymerase I mainly functions in removing RNA primers and filling in gaps, and DNA polymerase II is involved in DNA repair, but neither is the main enzyme for proofreading during replication.
5. Conclude that DNA polymerase III is the primary enzyme responsible for the bulk of DNA synthesis and possesses the 3\' to 5\' exonuclease activity needed for proofreading during prokaryotic DNA replication.