Which enzyme is responsible for removing RNA primers and replacing them with DNA during bacterial DNA replication?

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

Answer: (D)

RNA primers laid down by primase must be removed and replaced with DNA, and this job is carried out by DNA polymerase I. It has a 5' to 3' exonuclease activity that digests the RNA primers and a 5' to 3' polymerase activity that fills in the resulting gaps with DNA. After this replacement, DNA ligase seals the nick to create a continuous strand. The main replicative enzyme, DNA polymerase III, handles the bulk synthesis but lacks the exonuclease activity needed to remove primers. DNA polymerase II mainly participates in DNA repair, not primer removal.