To test this idea, we co-expressed a subset of the more severe SMA alleles with hexahistidine-FLAG-SUMO (HFS)-tagged SMNΔ5 and Gemin2, purified the complexes, and determined whether the untagged mutant proteins copurified with Ni-NTA beads (Figure 4C). The gene discussed is GEMIN2; the disease is proximal spinal muscular atrophy.