Effect of expression of hLigI51A and hLigI51D on the sensitivity of hLigI-deficient cells to a PARP inhibitor and MMS. Cultures of 46BR.1G1 cells either transfected with the empty vector (Vector) or expressing FLAG-tagged wild-type hLigI, hLigI51A (51A), or hLigI51D (51D) were grown in the presence of the indicated concentrations of the PARP inhibitor NU1025 (A) and the DNA alkylating agent MMS as described under “Experimental Procedures” (B). After 10 days, colonies were stained with crystal violet solution and then counted by using Quantity One 4.5. The graph shows data compiled from three independent experiments, with the error bars indicating S.D. *, p < 0.001) compared with cells expressing FLAG-tagged wild-type hLigI.