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.