FIG. 8.

Repair frequencies and DHFR activity. (A) Repair frequencies. Each repair-PPRH, previously incubated with the p11Mut plasmid in the DG44 cell line approach, was transfected into CHO cells. After 29–30 hr, cells were grown in selective medium to initiate the selection of repaired cells. The bars represent the frequency of cell colonies out of total cells seeded. Error bars indicate standard errors. Each assay was carried out a minimum of three times. (B) DHFR activity in repaired colonies from DG44, DG44p11Mut, and DA5 cells. Thirty thousand cells from each repair-PPRH approach were plated in 35 mm dishes and their DHFR activity was determined by the incorporation of 2 μCi of 6-[³H] deoxyuridine to the DNA. Cells were collected and lysed with SDS after 24 hr. Radioactivity was counted in a scintillation counter. The activity was determined in repaired individual clones obtained by the transient transfection into DG44, in stably DG44-p11Mut cells and in DA5 cell line. *p<0.05, **p<0.01, ***p<0.001 compared with the corresponding control.