The interplay between different repair mechanisms has long been a subject of significant interest.  We provide a direct demonstration that human DNA glycosylase hNEIL1 and the DNA damage-sensing factor XPC-RAD23B (XPC) competitively bind to the same oxidatively generated guanine lesions that are substrates of both Base Excision Repair (BER) and Nucleotide Excision Repair (NER) mechanisms. The binding of hNEIL1 and XPC proteins to 147 bp DNA duplexes was monitored by gel electrophoretic mobility shift assay (EMSA) methods. The competitive binding of these BER and NER factors is initially governed  by free diffusion mechanisms that determine the relative concentrations of the two different types of protein-DNA complexes formed after mixing. The binding of hNeil1 to its substrate is quickly followed by the irreversible endonuclease activity of this BER protein that precludes the subsequent participation of XPC in the repair process.  By contrast, if XPC binds to the lesion first, the lesion is not excised and remains intact until the subsequent NER factor TFIIH binds to the noncovalent [XPC-DNA] complex and excises the lesion.  However, if TFIIH is absent or its binding rate is slow, the equilibrium [XPC-DNA] ßà XPC + DNA briefly exposes the DNA upon the dissociation of XPC. If available in sufficient concentrations, hNEIL1 (or other proteins) bind to the free DNA lesions made available by the dissociation of XPC, thus enhancing the efficiency of the BER repair pathway. Preliminary results indicate that similar mechanisms can occur in intact mammalian cells.

Competitive binding of human DNA glycosylase hNEIL1 and DNA damage-sensing factor XPC-RAD23B to oxidatively generated guanine lesions

2019 Fall National Meeting

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