2,2,4-Triamino-5(2H)-oxazolone is a weak substrate for nucleotide excision repair

Abstract

Objective: 2,2,4‑Triamino‑5(2H)‑oxazolone (Oz) is a guanine lesion produced by
reactive oxygen radicals and photosensitized oxidation. This nucleobase is a potentially
mutagenic lesion, and is removed by several base excision repair enzymes. Our
purpose is to analyze whether Oz is the substrate of nucleotide excision repair (NER).
Materials and Methods: A lymphoblastoid cell line from the patient with xeroderma
pigmentosum (XP) complementation group C (XP3BE) was used. Cell‑free NER
reactions with covalently closed circular DNAs containing the Oz lesion were performed
using the XP3BE whole cell extracts with or without the XPC‑RAD23B complex.
In addition, DNA fragments (180 bp in length) containing the Oz lesion were used
for binding reactions with the XPC‑RAD23B complex. Results: We analyzed the
cell‑free NER activity on Oz and the binding affinity of XPC‑RAD23B, which initiates
NER. Human cell‑free NER activity on Oz was detected, though the reactivity to
Oz was lower than that on ultra violet (UV)‑induced pyrimidine (6‑4) pyrimidone
photoproduct (6‑4PP). Also, binding of XPC‑RAD23B with Oz was lower than that
with 6‑4PP. Conclusion: Because of the low binding affinity of Oz for XPC‑RAD23B,
NER efficiency on Oz is very low. Therefore, general NER is not the appropriate repair
system for Oz.