V79 (upper panel) and A549 cells (lower panel) were nontreated (NT) or treated with sense or antisense oligonucleotides to NEIL1, then treated with (+) or without (−) glucose oxidase (GO) for 1h to induce oxidative stress. NT, non-treated; S, sense oligonucleotide, AS, antisense oligonucleotide. The HPRT mutants were scored in 6-TG-containing HAT medium. The bar graphs represent the means ± standard error from 4 independent experiments.