A genetic screen for Saccharomyces cerevisiae mutants affecting proteasome function, using a ubiquitin-independent substrate.

The great majority of proteasome substrates are marked for degradation by the attachment of polyubiquitin chains. Ornithine decarboxylase is degraded by the proteasome in the absence of this modification. We previously showed that this mechanism of degradation was conserved in eukaryotic cells.