Question

Which of the following reactions is required for proofreading during DNA replication by DNA polymerase III?

(a) 5’ to 3’ exonuclease activity

(b) 3’ to 5’ exonuclease activity

(c) 3’ to 5’ endonuclease activity

(d) 5’ to 3’ endonuclease activity

Answer 1

Correct choice is (b) 3’ to 5’ exonuclease activity

To explain: The 3’ → 5’ exonuclease activity removes the mispaired nucleotide and the polymerase begins again. This activity is known as proofreading.