Figure 1.

Cells expressing catalytically inactive Lig4 or completely deficient in Lig4 are markedly sensitive to the DSB-inducing agents calicheamicin and teniposide. (A) Western blot of Lig4 in wild-type 293T cells (Lig4+/+), heterozygous cells (Lig4+/−), or 293T cells deficient in Lig4 (Lig4−/−), deficient in DNA-PKcs (DNA-PKcs−/−) or with mutations in Lig4 [K273A/−, and K273A*/−]. (These are two independent clones possessing one copy of catalytically inactive Lig4 and a frameshift mutation on the second Lig4 allele; the K273A clone containing an additional mutation, I270V is labelled K273A*/−, for brevity.). (B) Sensitivity of the same panel of cell strains to calicheamicin (B) or teniposide (C) was assessed. Briefly, cells were plated in 24 well plates into complete medium with increasing doses of calicheamicin or teniposide. After 7 days, MTT was added, and cell survival assessed by colorimetry. Survival assays were performed four times in duplicate (B) or three times in duplicate (C).