Proteasome dynamics between proliferation and quiescence stages of Saccharomyces cerevisiae

Abstract

The ubiquitin-proteasome system (UPS) plays a critical role in cellular protein homeostasis and is required for the turnover of short-lived and unwanted proteins, which are targeted by poly-ubiquitination for degradation. Proteasome is the key protease of UPS and consists of multiple subunits, which are organized into a catalytic core particle (CP) and a regulatory particle (RP). In Saccharomyces cerevisiae, proteasome holo-enzymes are engaged in degrading poly-ubiquitinated substrates and are mostly localized in the nucleus during cell proliferation. While in quiescence, the RP and CP are sequestered into motile and reversible storage granules in the cytoplasm, called proteasome storage granules (PSGs). The reversible nature of PSGs allows the proteasomes to be transported back into the nucleus upon exit from quiescence. Nuclear import of RP and CP through nuclear pores occurs via the canonical pathway that includes the importin-αβ heterodimer and takes advantage of the Ran-GTP gradient across the nuclear membrane. Dependent on the growth stage, either inactive precursor complexes or mature holo-enzymes are imported into the nucleus. The present review discusses the dynamics of proteasomes including their assembly, nucleo-cytoplasmic transport during proliferation and the sequestration of proteasomes into PSGs during quiescence.

Keywords:

• Proteasome
• yeast
• regulatory particle
• core particle
• quiescence
• proteasome storage granules
• ubiquitin
• substrate degradation

Acknowledgements

We put in our best efforts to cite original papers throughout the review and we sincerely apologize to all those whose contribution in the field of proteasome dynamics was left out unintentionally.

Disclosure statement

The authors report no declarations of interest.

Funding

This work was supported by the Canadian Institutes of Health Research [CIHR 325477] and the Natural Sciences and Engineering Research Council of Canada, 10.13039/501100000038 [NSERC 368298] to C.E.