Which statement best describes the proofreading capability of DNA polymerases in prokaryotes?

• A. DNA polymerases I and III have 3'→5' exonuclease proofreading
• B. DNA polymerase II alone provides proofreading
• C. No polymerase has proofreading
• D. DNA polymerases I and II have 3'→5' exonuclease proofreading

Answer: (B)

Proofreading during prokaryotic DNA replication relies on 3'→5' exonuclease activity to remove mismatched nucleotides as synthesis occurs. The primary copying enzyme, DNA polymerase III, provides most of this proofreading through its exonuclease function, greatly boosting fidelity. DNA polymerase I also has 3'→5' exonuclease proofreading, though its main roles are removing RNA primers and filling in gaps after Okazaki fragments rather than bulk synthesis. DNA polymerase II does have proofreading capability, but it is mainly involved in DNA repair rather than serving as the sole replicative proofreading enzyme. So proofreading in bacteria is a collaborative effort, with Pol III doing the bulk of it and Pol I contributing, while Pol II offers an additional, supportive role rather than being the sole source of proofreading.