Fig. 6
From: The endonuclease domain of the LINE-1 ORF2 protein can tolerate multiple mutations
Chronic expression of EN proteins containing mutations in putative phosphorylation sites causes toxicity. HeLa cells were transfected with a single expression plasmid containing both HygroR and the indicated EN putative phosphorylation mutant sequence. Hygromycin selection was maintained for 2 weeks post-transfection, allowing stable expression of ENp throughout the assay. EN is the functional protein and EN- is a non-functional protein containing inactivating mutations (D205A/H230A). Control indicates cells transfected with an empty vector. Colony formation was assayed after 2 weeks under hygromycin (Y-axis) and used as a measure of toxicity as previously described [27, 43]. Asterisks indicate a statistically significant difference in the relative number of HygroR colonies compared to EN (t-test, P ≤ 0.05)