N-Myristoylation of the Rpt2 Subunit Regulates Intracellular Localization of the Yeast 26S Proteasome

The 26S proteasome is a large, complex multisubunit protease involved in protein quality control and other critical processes in eukaryotes. More than 110 post-translational modification (PTM) sites have been identified by a mass spectrometry of the 26S proteasome of Saccharomyces cerevisiae and are predicted to be implicated in the dynamic regulation of proteasomal functions. Here, we report that the N-myristoylation of the Rpt2 subunit controls the intracellular localization of the 26S proteasome. While proteasomes were mainly localized in the nucleus in normal cells, mutation of the N-myristoylation site of Rpt2 caused diffusion of the nuclear proteasome into the cytoplasm, where it formed aggregates. In mutant cells, the level of accumulation of cytoplasmic proteasomes was significantly increased in the nonproliferating state. Although the molecular assembly and peptidase activity of the 26S proteasome were totally unchanged in the nonmyristoylated mutants of Rpt2, an increased level of accumulation of polyubiquitinated proteins and a severe growth defect were observed in mutant cells induced for protein misfolding. In addition, polyubiquitinated protein and the nuclear protein Gcn4 tended not to colocalize with the proteasome in normal and mutant cells. Our results suggest that N-myristoylation is involved in regulating the proper intracellular distribution of proteasome activity by controlling the nuclear localization of the 26S proteasome.