DNA replication (prokaryotes) – Which DNA polymerase removes RNA primers during DNA synthesis in bacteria such as E. coli?

Introduction:
During bacterial DNA replication, short RNA primers synthesized by primase must be removed and replaced with DNA. Recognizing the enzyme responsible for primer removal is essential for understanding lagging-strand processing and Okazaki fragment maturation.

Given Data / Assumptions:

• Primase synthesizes RNA primers to initiate DNA synthesis.
• Okazaki fragments on the lagging strand are RNA–DNA hybrids.
• Enzymes differ in exonuclease activities and processivity.

Concept / Approach:
E. coli DNA polymerase I possesses a unique 5'→3' exonuclease activity that removes RNA primers while simultaneously filling the resulting gaps with DNA (nick translation). DNA polymerase III is the main replicative enzyme but lacks the 5'→3' exonuclease for primer removal. DNA ligase subsequently seals remaining nicks by forming phosphodiester bonds.

Step-by-Step Solution:

Verification / Alternative check:
Mutants lacking DNA pol I 5'→3' exonuclease activity accumulate RNA primers and unprocessed Okazaki fragments, confirming the enzyme's specialized role in primer removal and gap filling.

Why Other Options Are Wrong:

• DNA pol II: involved in DNA repair and restart; lacks primer removal role.
• DNA pol III: high-processivity replication polymerase but lacks 5'→3' exonuclease.
• Primase: synthesizes primers; does not remove them.
• None of these: incorrect because DNA pol I is correct.

Common Pitfalls:
Assuming the main replicative polymerase (pol III) also removes primers; in bacteria, primer removal is a distinct function of pol I.

Final Answer:
DNA polymerase I