To examine the effects of UV irradiation on the development of CS phenotypes, we first compared cell growth before and after UV irradiation in 7 different rad2 deletion mutants, including those that mimic XPG mutations found in XPG and XPG/CS cells (supplementary material Fig. S1A; Table S1), to wild type (WT). This evidence concerns the gene FEN1 and Cowden syndrome 1.