Validation of the CYH2/cycloheximide counterselection. Plasmid repair was monitored as the recovery of Ura⁺ colonies for the control plasmid pRS316 (SmaI) or the test plasmid pCRG3 (SnaBI) in the presence or absence of an overlapping repair fragment. The cells were transformed by the LiAc/ssDNA/PEG method. Cycloheximide-resistant colonies were selected in the presence of 2.5 μg/mL of the drug.