The nuclear envelope is a barrier comprising outer and inner membranes that separate the cytoplasm from the nucleoplasm. The two membranes have different physical characteristics and protein compositions. The processes governing the stability of inner nuclear membrane (INM) proteins are not well characterized. In Saccharomyces cerevisiae, the INM Asi1–Asi3 complex, principally composed of integral membrane proteins Asi1 and Asi3, is an E3 ubiquitin ligase. In addition to its well-documented function in endoplasmic reticulum (ER)-associated degradation, the Doa10 E3 ubiquitin ligase complex partially localizes to the INM. The Asi1–Asi3 and Doa10 complexes define independent INM-associated degradation (INMAD) pathways that target discrete sets of nuclear substrates for proteasomal degradation. Here, we report that Asi1 is rapidly turned over (t1/2≤30 min). Its turnover depends on ubiquitin-mediated degradation by nucleus-localized proteasomes, exhibiting a clear requirement for the E2 ubiquitin-conjugating enzyme Ubc7, Cue1 and the AAA ATPase Cdc48 and co-factor Ubx1. Asi1 turnover occurs largely independently of the Asi1–Asi3 or Doa10 complexes, indicating that it is subject to quality control at the INM in a manner distinct from that of the characterized INMAD pathways.
The authors declare no competing or financial interests.
Conceptualization: M.P., M.B., P.O.L.; Methodology: M.P., M.B., P.O.L.; Formal analysis and investigation: M.P.; Writing – original draft preparation: M.P., P.O.L.; Writing – review and editing: M.P., M.B., R.F., P.O.L.; Visualization: M.P., P.O.L.; Supervision: R.F., P.O.L.; Project Administration: R.F., P.O.L.; Funding acquisition: M.B., R.F., P.O.L.
The authors acknowledge grant support from the Swedish Research Council (Vetenskapsrådet) [grant numbers VR-NT2011-5925 and VR-NT2015-04202 (P.O.L.)]; the Austrian Science Fund [FWF; grant number P23805-B20 (R.F.)]; and a European Molecular Biology Organization long-term fellowship (M.B.).
Supplementary information available online at http://jcs.biologists.org/lookup/doi/10.1242/jcs.189332.supplemental
- Received March 15, 2016.
- Accepted August 18, 2016.
- © 2016. Published by The Company of Biologists Ltd