Practice question

DNA polymerase I is unique among E. coli polymerases for possessing two distinct exonuclease activities within one polypeptide. Its 3' to 5' proofreading domain removes misincorporated nucleotides from growing strand, while N-terminal domain carries 5' to 3' exonuclease that cleaves RNA primers and downstream DNA during nick translation. Pol II possesses only 3' to 5' activity, Pol III epsilon provides proofreading but no 5' to 3' function. Dual nuclease capability qualifies Pol I for Okazaki fragment maturation, gap filling, and base excision repair patch removal.