sentence: Immunodetection of K164-monoubiquitylated PCNA forms in wild-type cells ( wt ) , GAL1-regulated overexpressing UBP10 cells ( wt * ) and GAL1-regulated overexpressing UBP10 ubp1 Δ ( 1 Δ ) to ubp17 Δ ( 17 Δ ) single mutant cells either reppressed ( OFF ) or induced ( ON ) for Ubp10 overexpression , after a 90 minutes treatment with 0.020 % MMS .