Fig. 1.

Survival of primary mouse fibroblasts after UV irradiation. The influence of mouse genotype on survival of primary dermal fibroblasts after irradiation with UV_{254 nm} was measured by colony-forming ability, as described in Methods. The fluence required to reduce the survival of Polη^+/+/ι^+/+ cells to 37% of the unirradiated control (D₃₇) was 8 J/m². This was reduced to ≈2.8 J/m² in the cells derived from Polη^−/−/ι^+/+. In both Polη^+/+ and Polη^−/− backgrounds, disruption of Polι slightly reduced UV survival. The significance of the reduced survival of pol ι-deficient cells was determined by polynomial regression analysis (53), with the best fit provided by cubic polynomials. This analysis revealed that the percent survival for Polη^+/+/ι^−/− cells was significantly lower than for Polη^+/+/ι^+/+ cells (P = 0.018), and that the percent survival for Polη^−/−/ι^−/− cells was significantly lower than for Polη^−/−/ι^+/+ cells (P = 0.001).