Ubiquitin+1 (Ub+1) is a novel mutant form of ubiquitin that can be produced through a process known as molecular frameshift. Ub+1 can be polyubiquitinated to produce aberrant polyubiquitin chains that inhibit the 26S proteasome. Especially ub+1 is accumulated in aggregates containing amyloid-beta and phosphorylated-tau. Elevated expression of Ub+1 mRNA and protein has been observed in the brains of patients with Alzheimer's disease. Also ub +1 acts as an aggravating factor in polyglutamine-induced neurodegeneration.