TABLE 1.
Effect of irradiation on CJ formation in wild-type and SCID thymic lymphoma cellsa
| Cell line | Expt no. | Irradiation | No. of Ampr | No. of Camr | %R | IR/C |
|---|---|---|---|---|---|---|
| VL3-3M2 | 1 | − | 2,610,000 | 124,000 | 4.75 | |
| 0.5 h (A) | 2,740,000 | 248,000 | 9.05 | 1.91 | ||
| LK6.2 | 1 | − | 154,000 | 615 | 0.40 | |
| 0.5 h (B) | 106,000 | 2,260 | 2.13 | 5.34 | ||
| 0.5 h (A) | 247,000 | 4,350 | 1.76 | 4.41 | ||
| LK3C | 1 | − | 69,300 | 142 | 0.20 | |
| 0.5 h (B) | 12,300 | 77 | 0.63 | 3.06 | ||
| VL3-3M2 | 2 | − | 398,000 | 29,600 | 7.4 | |
| 0.5 h (B) | 192,000 | 13,800 | 7.2 | 0.97 | ||
| LK6.2 | 2 | − | 439,000 | 2,480 | 0.6 | |
| 0.5 h (B) | 9,600 | 225 | 2.3 | 4.15 | ||
| VL3-3M2 | 3 | − | 1,260,000 | 8,140 | 0.65 | |
| 0.5 h (B) | 2,510,000 | 50,000 | 1.99 | 3.08 | ||
| LK6.2 | 3 | − | 929,000 | 429 | 0.05 | |
| 0.5 h (B) | 121,000 | 964 | 0.80 | 17.25 | ||
| LK8 | 3 | − | 1,870,000 | 694 | 0.04 | |
| 0.5 h (B) | 379,000 | 411 | 0.11 | 2.92 |
The efficiency of CJ formation was measured as percent recombination (%R) for each cell line as described in Materials and Methods. Briefly, 40 to 48 h after transient transfection with pDR42, plasmid DNA harvested from each cell line was electroporated into E. coli. The percent recombination (%R) was calculated as the ratio (×100) between the number of colonies resistant to ampicillin (Ampr) and those resistant to ampicillin plus chloramphenicol (Camr). Cell lines were treated with 100 cGy of γ-irradiation at the indicated times before (B) or after (A) transfection with pDR42. The number of cells recovered after 48 h did not vary more than twofold within each group. The effect of irradiation on the efficiency of CJ formation was calculated as the ratio of recombination frequencies of irradiated cultures to those of control cultures (IR/C). −, no irradiation.