Question

Repair of an apurinic or apyrimidinic site in DNA by AP endonuclease must be completed by the action of _________.

1) UvrABC endonuclease
2) RecA protein
3) DNA polymerase I
4) None of the choices are correct

Answer 1

The repair of an AP site in DNA by AP endonuclease is completed by the action of DNA polymerase I, which replaces the missing nucleotide and prepares the DNA for sealing by DNA ligase.

Step-by-step explanation:

The repair of an apurinic or apyrimidinic (AP) site in DNA by AP endonuclease is a crucial step in the base excision repair pathway. After AP endonuclease recognizes and nicks the DNA at the site of the missing base, the repair must be completed by the action of DNA polymerase I. DNA polymerase I plays a distinct role in DNA repair by removing the damaged section with its 5' exonuclease activity and then adding the correct nucleotide to the 3' end of the nick. Finally, the DNA strand is sealed with a phosphodiester linkage, which is catalyzed by DNA ligase to complete the repair process. Therefore, the correct answer is 3) DNA polymerase I.