A 10 year old child experiences recurrent skin lesions on her face and upper extremities that rapidly progress to cancer. Xeroderma pigmentosa is considered a possible differential. Which of the following is defective in that case
Topoisomerase
3' → 5' Exonuclease
Endonuclease
Helicase
UV rays damage DNA by forming thymidine dimers. This is repaired by the body by nucleotide excision repair. Main enzyme of this mechanism is UV-specific endonuclease.