a, Left, SDS–PAGE analysis followed by Coomassie blue staining of His-tagged human SLC19A1 (purified on Ni-NTA) pull-downs with Sepharose beads coupled with 2′3′-cGAMP (+) or control Sepharose beads (−). Input is shown on the right. b, Western blots of the samples in a with SLC19A1 antibody. c, Pull-downs of SLC19A1 competed with CDNs. His-tagged SLC19A1 was incubated with no CDN or with the indicated competing CDNs (250 µM) before pull-downs with 2′3′-cGAMP-Sepharose, followed by SDS–PAGE and western blotting with SLC19A1 antibody. A pulldown with control Sepharose is shown for comparison. For gel source data, see Supplementary Fig. 1. d, SDS–PAGE analysis followed by Coomassie blue staining of pull-downs of mSTING CTD with 2′3′-cGAMP (+) or control (−) Sepharose. In all panels, data are representative of two independent experiments with similar results.