Alkylating agents are commonly used as anticancer drugs. DNA methylation predominantly occurs at the N7 position of guanine (N7mdG). N7mdG hydrolyzes to yield an abasic site (AP) with a half life of ~102-190 h in naked DNA. However, N7mdG reactivity in nucleosome core particles (NCPs) has not been reported. We reconstituted NCPs containing N7mdG at specific positions. N7mdG depurination in NCPs is ~1.3-5.7 fold slower than in naked DNA. Larger decreases in depurination rates were observed when N7mdG is proximal to the histone tails. Experiments using mutated proteins indicate that the histone tails are responsible for the majority of the decreased depurination rates. Importantly, we discovered that the histone protein tails form DNA-protein crosslinks (DPCs) with N7mdG, and the yields of DPCs are comparable to the amounts of AP. To our knowledge, DPCs have never been reported from monoalkylation agents in chromatin. The formation of DPCs from N7mdG suggests an alternative mechanism for the cytotoxicity of monofunctional DNA alkylating agents.<br/>

Histone protein tails inhibit depurination of N7-methylated deoxyguanosine and form DNA-protein crosslinks with alkylated DNA in nucleosome core particles

254th National Meeting (2017)

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