What is the role of DNA polymerase I in prokaryotic replication?

• A. It seals nicks in the sugar-phosphate backbone.
• B. It unwinds the DNA ahead of replication.
• C. It replaces RNA primers with DNA and participates in nick translation with 5' to 3' exonuclease activity.
• D. It synthesizes RNA primers.

Answer: (C)

DNA polymerase I’s job in prokaryotic replication is to clean up the RNA primers and replace them with DNA. It uses its 5' to 3' exonuclease activity to remove the RNA primer while its 5' to 3' polymerase activity adds DNA in its place. This coordinated action, called nick translation, fills in the gaps left after primer removal so the DNA backbone can be continuous. After this, DNA ligase seals the remaining nick to finish the connection.

Think of it as the cleanup crew after the primers are laid: primers are made by primase, the main elongation is done by DNA polymerase III, the primer is removed and replaced by Pol I, and the final nick is sealed by ligase. The other activities listed belong to different enzymes: unwinding ahead of the fork is done by helicase, and synthesizing RNA primers is the job of primase.