Purified PA200-bound proteasomes have been shown to degrade histones (Qian et al, 2013), and in human cells, the knockdown of PA200 reduces the degradation of histones (Mandemaker et al, 2018) and mutant aggregation-prone proteins that cause neurodegenerative diseases (Aladdin et al, 2020). This evidence concerns the gene PSME4 and neurodegenerative disease.