C: Left panel: Ubc9 D100A enhances sensitivity to Ara-C or etoposide. Cell survival assays were performed as described in Fig. 5C. Cells were exposed to Ara-C or etoposide (VP16) for 1 h and evaluated 10 days later. Right panel: N-acetylcysteine treatment rescues the higher toxicity of Ara-C or etoposide on "Ubc9 DA" cells. Cells were treated with 0.5 mM NAC 16 h prior to addition of etoposide or Ara-C. Graphs represent means of three to four independent experiments, error bars represent S.E.M. * p < 0.05. 