HR and NHEJ reporter assays

Homologous recombination (HR) and NHEJ repair in HEK293T cells were measured as described previously using the DR‐GFP stable cells (Pierce et al, 2001) and EJ5‐GFP stable cells (Bennardo et al, 2008). Briefly, 0.5 × 10⁶ HEK293T stable reporter cells were seeded in 6‐well plates co‐transfected with 2 μg I‐SceI expression plasmid (pCBASce) and either 4 μg pcDNA‐hcGAS mutants or empty pcDNA vector. Forty‐eight hours post‐transfection, cells were harvested and analyzed by flow cytometry analysis for GFP expression. Means were obtained from three independent experiments. U2OS cells silenced for using cGAS were transfected with 2 μg I‐SceI expression plasmid (pCBASce) for 2 days, then harvested and analyzed by flow cytometry analysis for GFP expression.