Full-length cDNAs for three human proteasome activator subunits, called REGα, REGβ, and
REGγ, have been expressed in Escherichia coli, and the purified recombinant proteins have
been characterized. Recombinant α or γ subunits form heptameric species; recombinant β
subunits are found largely as monomers or small multimers. Each recombinant REG
stimulates cleavage of fluorogenic peptides by human red cell proteasomes. The pattern of
activated peptide hydrolysis is virtually identical for REGα and REGβ. These two subunits …