Which of the following enzymes in DNA replication possesses exonuclease activity in prokaryotes (E. coli), essential for removing RNA primers during Okazaki fragment maturation?
Answer and explanation
Correct answer: D. DNA Polymerase I
- Step 1: Review prokaryotic polymerase activities: DNA Polymerase III is the primary replicative polymerase possessing polymerase and proofreading exonuclease activities, but lacks exonuclease capability.
- Step 2: DNA Polymerase I uniquely possesses an additional exonuclease domain that degrades RNA primers ahead of the enzyme (nick translation) while simultaneously synthesizing replacing DNA in the direction.
Answer
DNA Polymerase I.
Why not the others: DNA Polymerase III lacks exonuclease function and cannot excise RNA primers; DNA Ligase catalyzes phosphodiester bond formation between adjacent fragments but lacks nuclease activity; Topoisomerase II (DNA Gyrase) relieves torsional supercoiling by introducing transient double-strand breaks.
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