FLAG-cGAS IP followed by quantitative PCR was performed as described previously (White et al., 2014 (link)). In brief, WT and Ngly1−/− MEFs were transduced or transiently transfected with a plasmid encoding FLAG-tagged cGAS. Dynabeads Protein G (10004D; Thermo Fisher Scientific) were conjugated with mouse monoclonal anti-FLAG M2 antibody (F1804; Sigma-Aldrich) or isotype mouse-IgG (I5381; Sigma-Aldrich) at 4°C overnight. Immunoprecipitation was performed following standard protocol. Before DNA extraction, a fraction of beads was eluted using loading buffer and boiled for 5 min to confirm FLAG-cGAS precipitation by Western blot. Protein G beads were treated with 200 µg/ml protease K (Ambion) at 55°C for 30 min to release bound DNA. Co-precipitated DNA were examined by quantitative PCR and normalized to IP FLAG-cGAS. Primer sequences of mitochondrial genes are used as described previously (West et al., 2015 (link)).