Negative-stain electron micrographs of cGAS•dsDNA complexes. (A, E) 3-fold excess cGAS over dsDNA, (B, F) 3-fold excess dsDNA over cGAS, (C, G) 3-fold excess K349E-cGAS over dsDNA, (D, H) 3-fold excess dsDNA over K394E-cGAS. Ratios of protein to dsDNA or dsDNA to protein are binding site normalized; 18 bp per binding site. The particle sizes in B and F are consistent with the Dmax of cGAScat and cGASFL, respectively (Figures 1 and 4). Particle sizes in C and H are consistent with the Dmax of K394E-cGAS variants (Figure 5—figure supplement 1).