Which type of DNA polymerase is essential for removing RNA primers and replacing them with nucleotides?

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

Answer: (A)

Removing RNA primers and replacing them with DNA hinges on a special capability: the enzyme must be able to chew away RNA primers and then fill the resulting gap with DNA. In bacteria, that job is done by DNA polymerase I because it has a 5' to 3' exonuclease activity to remove the RNA primers and a 5' to 3' polymerase activity to lay down the new DNA. After the replacement, DNA ligase seals the remaining nick, completing the process.

Other polymerases don’t perform this primer-removal step. DNA polymerase III is the main workhorse that synthesizes DNA, but it lacks the 5' to 3' exonuclease needed to remove RNA primers. Polymerases II and IV are more involved in repair and bypass tasks rather than primer removal during replication.