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Supporting Text

A 16-mer DNA, 5'-AGCGTCCAXGTCTACC-3', where X denotes 8-oxoguanine (oxoG), was labeled at the 5' terminus with T4 polynucleotide kinase (T4 PNK, New England Biolabs) in 1X T4 PNK buffer supplemented with 2 ml. g[³²P]-ATP, 10 mCi/ml (10,000 Ci/mmol, New England Nuclear). T4 PNK was heat denatured and the radiolabeled DNA was annealed to 1.1 fold excess of complementary strand, 5'-TGGTAGACCTGGACGC -3'. The cleavage assays were typically performed in 100 ml. reaction volume with 200 nM protein and 20 nM labeled duplex DNA in 50 mM NaCl, 50 mM Tris pH 7.4 at 25°C. The reactions were quenched by withdrawing 10 ml samples and adding to equal volume of 95% formamide in 1X TBE. Cleaved DNA was resolved from uncleaved DNA on a 20% urea-PAGE gel and viewed by PhosphorImaging.