We engineered synthetic genes that fused ascorbate peroxidase 2 (APEX2) to human wild-type FUS (FUS WT), FUS PM, or the ALS-linked mutant P525L (FUS P525L [FUS proline 525 to leucine mutant]) to enable proximity-dependent biotinylation of potential protein-binding partners (51). Here, APEX2 is linked to amyotrophic lateral sclerosis.