Final answer:
The 3' exonuclease subunit of DNA polymerase III corrects mistakes during DNA replication by excising incorrectly paired bases and allowing the insertion of the correct ones.
Step-by-step explanation:
The 3' exonuclease activity of DNA polymerase III is responsible for the proofreading and correction of mistakes during DNA replication. DNA polymerase III checks the newly added base against the template strand and excises the incorrectly paired base if needed, allowing for the correct base to be added subsequently. This function is crucial because it maintains the DNA replication process's high fidelity, ensuring genetic information is copied accurately.