Since POLD1 KD MDA-MB-231 cells were not able to form colonies for HPRT assay (Supplementary Fig. 3n), we instead established MIF KO in colorectal cancer cell line DLD1 cells, which have Pol δ mutations R689W and R506H in the conserved DNA polymerase III and exonuclease III motifs, respectively32. Here, POLD1 is linked to colorectal cancer.