Figure 5. DNA ligase IV and Artemis deletion independently contribute to increased cellular resistance to replication-induced DSBs and increased gene targeting.

(A, B) Sensitivity of wild-type, ARTEMIS ^−/−, LIG4 ^−/−, and LIG4 ^−/− ARTEMIS ^−/− cells to CPT (A) and NU1025 (B), as determined by growth inhibition assays. Symbols are as in Figure 4. Data are the mean ± SD of three independent experiments. Where absent, error bars fall within symbols. (C) Gene-targeting efficiency of wild-type, ARTEMIS ^−/−, LIG4 ^−/−, and LIG4 ^−/− ARTEMIS ^−/− cells. The gene-targeting efficiency at the HPRT locus was determined by the ratio of the number of targeted clones to that of clones analyzed.