Cytosolic ubiquitin protein

Hill K, Cooper AA (2000) Degradation of unassembled Vphlp reveals novel aspects of the yeast ER quality control system. EMBO J 19 550-561 Hiller MM, Finger A, Schweiger M, Wolf D H (1996) ER degradation of a misfolded luminal protein by the cytosolic ubiquitin-proteasome pathway. Science 273 1725-1728... 

Matunis, M. j., Coutavas, E., and Blobel, G., a novel ubiquitin-like modification modulates the partitioning of the Ran-GTPase-activating protein RanGAPl between the cytosol and the nuclear pore complex,/. Cell. Biol., 1996, 135, 1457. 

Protein processing in the endoplasmic reticulum makes mistakes. All membrane-associated proteins and proteins that are secreted by the cell are synthesised on membrane-bound ribosomes and pass into the lumen of the reticulum, where they are modified by post-translational processes, so that much biochemical manipulation of the proteins takes place. Consequentially mistakes are often made. Such abnormal proteins are exported from the lumen into the cytosol for ubiquitination and degradation in the proteasome. 

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