DNA polymerase (pol) ϵ is essential for DNA replication and is thought to be a component of DNA repair systems in eukaryotic cells. The activities of pol ϵ have been examined using a series of synthetic oligonucleotides designed with cis-diamminedichloroplatinum(II) (cis-DDP)-modified specific guanine residues. Pol ϵ was incapable of synthesis over cis-DDP-modified single guanine or adjacent guanine residues present in the template strand. Both single and double guanines modified by cis-DDP present at the 3′-OH end of a primer strand completely inhibited the synthetic activity of pol ϵ and, in addition, sequestered pol ϵ at the platinated 3′-OH termini. The sequestering of pol ϵ on cis-DDP modified DNA may interfere with the function of this enzyme in DNA repair in vivo. The intrinsic 3′ to 5′ proofreading exonuclease activity of pol e was also examined. Pol ϵ was capable of degrading a single-strand template with internal cis-DDP-modified guanines up to, but not through, the platinated nucleotides. A single platinated guanosine was sufficient to block the 3′ to 5′ exonuclease activity of pol ϵ. These results suggest that cis-DDP-DNA adducts inhibit DNA synthesis mediated by DNA polymerase ϵ and that platinated sites can arrest the nuclease of pol ϵ, a function exhibited during DNA repair.
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