We fused APEX2 to the N terminus of three FUS protein variants via a (GGGS)3-FLAG tag linker to generate three Twin-Strep-tagged constructs: (1) FUS WT, (2) FUS PM, and (3) the ALS-linked FUS P525L (Fig. 1, A and B). The gene discussed is APEX2; the disease is amyotrophic lateral sclerosis.