In Escherichia coli DNA repair, which DNA polymerase primarily fills short gaps during nucleotide-excision repair and Okazaki fragment processing because it has 5'→3' exonuclease activity?

Introduction / Context:
E. coli encodes several DNA polymerases with distinct roles. Understanding which enzyme participates in repair versus replication is crucial for interpreting mutant phenotypes and biochemical assays.

Given Data / Assumptions:

• Bacterial system (E. coli), not eukaryotes.
• Short single-stranded gaps arise after primer removal and during excision repair.
• An enzyme with both polymerase activity and 5'→3' exonuclease is advantageous for removing RNA primers and damaged nucleotides ahead of synthesis.

Concept / Approach:
DNA polymerase I possesses 5'→3' exonuclease activity that can remove RNA primers and excised oligonucleotides while simultaneously filling the gap with DNA. Polymerase III is the main replicative polymerase but lacks prominent 5'→3' exonuclease; Pol II is involved in repair under stress but is not the primary enzyme for primer removal.

Step-by-Step Solution:

Verification / Alternative check:
Classic experiments with Pol I mutants (polA) and biochemical nick-translation assays demonstrate its 5'→3' exonuclease and repair roles, while Pol III functions as the high-processivity replicase.

Why Other Options Are Wrong:

• DNA polymerase II: Participates in repair and restart but lacks the principal 5'→3' exonuclease-driven nick translation function.
• DNA polymerase III holoenzyme: Main replicative polymerase; high processivity but not specialized for primer removal.
• None of these: Incorrect because Pol I fits the described function.
• Telomerase: Eukaryotic enzyme for telomere extension, absent in E. coli.

Common Pitfalls:
Assuming the major replicative polymerase also performs most repair gap-filling, or confusing 3'→5' proofreading with 5'→3' exonuclease used in nick translation.

Final Answer:
DNA polymerase I.