1. Pfanner, N., Warscheid, B. & Wiedemann, N. Mitochondrial proteins: from biogenesis to functional networks. Nat. Rev. Mol. Cell Biol. 20, 267–284 (2019).

2. Neupert, W. & Herrmann, J. M. Translocation of proteins into mitochondria. Annu. Rev. Biochem. 76, 723–749 (2007).

3. Endo, T. & Yamano, K. Multiple pathways for mitochondrial protein traffic. Biol. Chem. 390, 723–730 (2009).

4. Boos, F. et al. Mitochondrial protein-induced stress triggers a global adaptive transcriptional programme. Nat. Cell Biol. 21, 442–451 (2019).

5. Pickles, S., Vigié, P. & Youle, R. J. Mitophagy and quality control mechanisms in mitochondrial maintenance. Curr. Biol. 28, R170–R185 (2018).

6. Shpilka, T. & Haynes, C. M. The mitochondrial UPR: mechanisms, physiological functions and implications in ageing. Nat. Rev. Mol. Cell Biol. 19, 109–120 (2018).

7. Wrobel, L. et al. Mistargeted mitochondrial proteins activate a proteostatic response in the cytosol. Nature 524, 485–488 (2015).

8. Wang, X. & Chen, X. J. A cytosolic network suppressing mitochondria-mediated proteostatic stress and cell death. Nature 524, 481–484 (2015).

9. Weidberg, H. & Amon, A. MitoCPR – a surveillance pathway that protects mitochondria in response to protein import stress. Science 360, eaan4146 (2018).

10. Bausewein, T. et al. Cryo-EM structure of the TOM core complex from Neurospora crassa. Cell 170, 693–700.e7 (2017).

11. Neuber, O., Jarosch, E., Volkwein, C., Walter, J. & Sommer, T. Ubx2 links the Cdc48 complex to ER-associated protein degradation. Nat. Cell Biol. 7, 993–998 (2005).

12. Schuberth, C. & Buchberger, A. Membrane-bound Ubx2 recruits Cdc48 to ubiquitin ligases and their substrates to ensure efficient ER-associated protein degradation. Nat. Cell Biol. 7, 999–1006 (2005).

13. Zahedi, R. P. et al. Proteomic analysis of the yeast mitochondrial outer membrane reveals accumulation of a subclass of preproteins. Mol. Biol. Cell 17, 1436–1450 (2006).

14. Wang, C.-W. & Lee, S. C. The ubiquitin-like (UBX)-domain-containing protein Ubx2/Ubxd8 regulates lipid droplet homeostasis. J. Cell Sci. 125, 2930–2939 (2012).

15. Becker, T. et al. The mitochondrial import protein Mim1 promotes biogenesis of multispanning outer membrane proteins. J. Cell Biol. 194, 387–395 (2011).

16. Papić, D., Krumpe, K., Dukanovic, J., Dimmer, K. S. & Rapaport, D. Multispan mitochondrial outer membrane protein Ugo1 follows a unique Mim1-dependent import pathway. J. Cell Biol. 194, 397–405 (2011).

17. Backes, S. et al. Tom70 enhances mitochondrial preprotein import efficiency by binding to internal targeting sequences. J. Cell Biol. 217, 1369–1382 (2018).

18. Bodnar, N. O. et al. Structure of the Cdc48 ATPase with its ubiquitin-binding cofactor Ufd1–Npl4. Nat. Struct. Mol. Biol. 25, 616–622 (2018).

19. Heo, J.-M. et al. A stress-responsive system for mitochondrial protein degradation. Mol. Cell 40, 465–480 (2010).

20. Wu, X., Li, L. & Jiang, H. Doa1 targets ubiquitinated substrates for mitochondria-associated degradation. J. Cell Biol. 213, 49–63 (2016).

21. Okreglak, V. & Walter, P. The conserved AAA-ATPase Msp1 confers organelle specificity to tail-anchored proteins. Proc. Natl Acad. Sci. USA 111, 8019–8024 (2014).

22. Chen, Y. C. et al. Msp1/ATAD1 maintains mitochondrial function by facilitating the degradation of mislocalized tail-anchored proteins. EMBO J. 33, 1548–1564 (2014).

23. Izawa, T., Park, S.-H., Zhao, L., Hartl, F. U. & Neupert, W. Cytosolic protein Vms1 links ribosome quality control to mitochondrial and cellular homeostasis. Cell 171, 890–903.e18 (2017).

24. Tran, J. R. & Brodsky, J. L. The Cdc48–Vms1 complex maintains 26S proteasome architecture. Biochem. J. 458, 459–467 (2014).

25. Schuberth, C., Richly, H., Rumpf, S. & Buchberger, A. Shp1 and Ubx2 are adaptors of Cdc48 involved in ubiquitin-dependent protein degradation. EMBO Rep. 5, 818–824 (2004).

26. van der Laan, M. et al. Pam17 is required for architecture and translocation activity of the mitochondrial protein import motor. Mol. Cell. Biol. 25, 7449–7458 (2005).

27. Bömer, U. et al. The sorting route of cytochrome b 2 branches from the general mitochondrial import pathway at the preprotein translocase of the inner membrane. J. Biol. Chem. 272, 30439–30446 (1997).

28. Verma, R. et al. Vms1 and ANKZF1 peptidyl-tRNA hydrolases release nascent chains from stalled ribosomes. Nature 557, 446–451 (2018).

29. Zurita Rendón, O. et al. Vms1p is a release factor for the ribosome-associated quality control complex. Nat. Commun. 9, 2197 (2018).

30. Ast, T., Michaelis, S. & Schuldiner, M. The protease Ste24 clears clogged translocons. Cell 164, 103–114 (2016).

31. Wenz, L. S. et al. Sam37 is crucial for formation of the mitochondrial TOM–SAM supercomplex, thereby promoting β-barrel biogenesis. J. Cell Biol. 210, 1047–1054 (2015).

32. Ellenrieder, L. et al. Separating mitochondrial protein assembly and endoplasmic reticulum tethering by selective coupling of Mdm10. Nat. Commun. 7, 13021 (2016).

33. Longtine, M. S. et al. Additional modules for versatile and economical PCR-based gene deletion and modification in Saccharomyces cerevisiae. Yeast 14, 953–961 (1998).

34. Morgenstern, M. et al. Definition of a high-confidence mitochondrial proteome at quantitative scale. Cell Reports 19, 2836–2852 (2017).

35. Janke, C. et al. A versatile toolbox for PCR-based tagging of yeast genes: new fluorescent proteins, more markers and promoter substitution cassettes. Yeast 21, 947–962 (2004).

36. Kushnirov, V. V. Rapid and reliable protein extraction from yeast. Yeast 16, 857–860 (2000).

37. Opaliński, Ł. et al. Recruitment of cytosolic J-proteins by TOM receptors promotes mitochondrial protein biogenesis. Cell Reports 25, 2036–2043.e5 (2018).

38. Schuler, M. H., Di Bartolomeo, F., Mårtensson, C. U., Daum, G. & Becker, T. Phosphatidylcholine affects inner membrane protein translocases of mitochondria. J. Biol. Chem. 291, 18718–18729 (2016).

39. Wittig, I., Braun, H. P. & Schägger, H. Blue native PAGE. Nat. Protocols 1, 418–428 (2006).

40. Haan, C. & Behrmann, I. A cost effective non-commercial ECL-solution for western blot detections yielding strong signals and low background. J. Immunol. Methods 318, 11–19 (2007).

41. Emanuelsson, O., Brunak, S., von Heijne, G. & Nielsen, H. Locating proteins in the cell using TargetP, SignalP and related tools. Nat. Protocols 2, 953–971 (2007).

42. Neal, S. et al. The Dfm1 derlin is required for ERAD retrotranslocation of integral membrane proteins. Mol. Cell 69, 306–320.e4 (2018).