Fig 1: AltFUS/ FUS stoichiometry in human brain lysates Estimation of the concentration of GFP‐FUS and GST‐altFUS recombinant proteins (10 μL loaded each). A commercial LSD1 recombinant protein diluted at 0.2 μg/μL was used as standard. The concentration for GFP‐FUS was evaluated to 0.06 μg/μL and that of GST‐altFUS was evaluated to 0.07 μg/μl.Western blot of human brain lysates spiked with GFP‐FUS (last lane). The recombinant protein alone (first lane) and a whole cell lysate of HEK293 cells were used as size controls. The bands corresponding to the recombinant GFP‐FUS and to the endogenous FUS proteins are indicated on the left. Immunoblot: anti‐FUS (Abcam, ab84078).Western blot of human brain lysates spiked with GST‐altFUS (last lane). The recombinant protein alone (first lane) and a whole cell lysate of HEK293 cells were used as size controls. The bands corresponding to the recombinant GST‐altFUS and to the endogenous altFUS proteins are indicated on the left. The asterisk indicates a protein species detected with the anti‐altFUS antibody specifically in the brain (see Fig 2C–E). Immunoblot: custom anti‐altFUS.