Figure 4.

Stabilization of short-lived proteasome substrates. WT and the S119A mutant strains containing the Ub-Met-, Ub-Arg-, and Ub-Pro-βgal constructs on multi-copy plasmids under the GAL promotor were tested for LacZ activity after galactose-induction. LacZ activity is indicative of steady-state levels of the reporter protein. WT cells accumulate high levels of the stable Met-βgal, but rapidly degrade Arg-βgal and UB-Pro-βgal (left panel), whereas the MPN+ mutation shows dramatic stabilization and accumulation of both short-lived fusion proteins (right panel).