(A) The HA-tagged A4V SOD1 interacted with the segment of p62 encoded by exons 4 and 5 only when it was tagged with the tetrameric DsRedT, but not the monomeric DsRedM. The indicated DsRed-tagged p62 constructs were co-transfected with HA-tagged A4V SOD1, and cellular extracts were subjected to HA immunoprecipitation. (B). The HA-tagged A4V SOD1 interacted with the DsRedT-exon 4, but not DsRedT-exon 5. The sequence encoded by exon 4 was termed as the SOD1 mutant interaction region (SMIR). (C). The DsRedT-tagged SMIR was co-immunoprecipitated with multiple ALS-linked SOD1 mutants (A4V, G37R, G85R and G93A) tagged with HA, but not with WT SOD1.