Many details of structure, function and substrate specificity of eukaryotic proteasomal systems have been elucidated. This information far-exceeds that available for the archaeal and bacterial counterparts. While structural and functional studies have provided some insight into the workings of prokaryotic proteasomes, the question of substrate targeting and global cellular influence remain largely unaddressed. In this communication, we report an over 720-fold increase in the half-life of the DNA-sliding clamp protein proliferating cell nuclear antigen after knockout of the panA gene, encoding a proteasome-activating nucleotidase A, on the chromosome of the halophilic archaeon Haloferax volcanii. This discovery marks the first identification of a protein stabilized by an archaeal proteasome mutation and provides a starting point for investigations into substrate recognition mechanisms. The findings also begin to address the functional role of proteasomal systems within the scope of the archaeal cell.