Nucleated cell-cell fusion, experiments were performed as described31,32. Calcein-AM was loaded into effector cells expressing the fusion protein, and 7-amino-4-chloromethylcoumarin (CMAC) was loaded into target cells. Mixing of dyes was scored as fusion. Fusion experiments for each viral protein were performed as previously described: EBOV GP32; HIV33; SFV E1/E2 and IAV HA34; VEEV E, VSV, and EBV35. Unless stated otherwise, EBOV GP was used as the fusion protein and C15:1 GA was used to inhibit fusion. As shown in Fig. 2B, C15:1 GA inhibited fusion for the eight tested fusion proteins. Figure 2C documents that fusion was blockaded by GA C13:0, C15:1, or C17:1.