ATR and cancer: To identify potential synthetically lethal interactions between ATR and certain DNA-repair genes, we compared the effects of siRNA-mediated knockdown of single genes on the proliferation rate of ATR-proficient parental versus ATR-deficient ATRs/s DLD1 cancer cells harboring the ATR knock-in Seckel mutation [23], using a focused siRNA library directed against 288 DNA repair genes each targeted by three different siRNAs.