Expression of x-irradiated prokaryotic genes after transfection in primate cells

X-irradiated rhoSC2CAT plasmids were transfected into monkey CV-1 and COS-7 cells and human fibroblast cells. Transient expression assays for chloramphenicol acetyltransferase (CAT) showed that expression from irradiated plasmids decreased with the same D/sub o/ as the x-ray conversion of circular forms to linear molecules of unit length, i.e., 13 Gy after irradiation in water or 270 Gy after irradiation in 1 mM Tris buffer. Loss of supercoiled forms was complete at much lower radiation doses than were required to inhibit CAT expression. In rhoSV2CAT one radiation linearization event after x-irradiation in water was associated with 6.5 single strand breaks. A single linearization event by Bam H1 at a site outside the CAT gene reduced CAT expression to 5% of control values, suggesting that circular or supercoiled plasmids are favored for expression. Expression of irradiated plasmids in cell lines established from patients with ataxia telangiectasia (AT), xeroderma pigmentosum (XP), and from normal subjects were compared. Certain repair deficient cell lines exhibited markedly reduced capacity to express unirradiated or irradiated pSV2CAT. The results indicate a useful new way to judge the complete expression of genes after minimal x-ray damage to the DNA, by introducing the genes into unirradiated cells of differing DNA repair capacities