An unphosphorylatable mutant S. cerevisiae IDR with identical basal net charge to the wild type (“WT-charge” mutant) recapitulates wild-type morphology and pFUS1 expression. (A) Amino acid sequence of the WT-charge mutant IDR, with mutated phosphorylation sites highlighted in red when mutated to alanine and orange when mutated to glutamic acid. (B) Mean pFUS1-gfp expression for wild-type (WT), 5A mutant (5A), and WT-charge mutant IDRs. Error bars represent 1.96 SE of three biological replicates. (C) Example brightfield (BF) micrographs from WT, 5A, and WT-charge mutant IDR strains.