UMMS Affiliation

Department of Biochemistry and Molecular Pharmacology

Publication Date


Document Type



Biochemistry, Biophysics, and Structural Biology


The yeast endoplasmic reticulum has three distinct protein translocation channels. The heterotrimeric Sec61 and Ssh1 complexes, which bind translating ribosomes, mediate cotranslational translocation of proteins targeted to the endoplasmic reticulum by the signal recognition particle (SRP) and SRP receptor targeting pathway, whereas the heptameric Sec complex has been proposed to mediate ribosome-independent post-translational translocation of proteins with less hydrophobic signal sequences that escape recognition by the SRP. However, multiple reports have proposed that the Sec complex may function cotranslationally and be involved in translocation or integration of SRP-dependent protein translocation substrates. To provide insight into these conflicting views, we induced expression of the tobacco etch virus protease to achieve rapid inactivation of the Sec complex by protease-mediated cleavage within the cytoplasmic domain of the Sec63 protein. Protein translocation assays conducted after tobacco etch virus protease induction revealed a complete block in translocation of two well-characterized substrates of the Sec complex, carboxypeptidase Y (CPY) and Gas1p, when the protease cleavage sites were located at structural domain boundaries in Sec63. However, integration of SRP-dependent membrane protein substrates was not detectably impacted. Moreover, redirecting CPY to the cotranslational pathway by increasing the hydrophobicity of the signal sequence rendered translocation of CPY insensitive to inactivation of the Sec complex. We conclude that the Sec complex is primarily responsible for the translocation of yeast secretome proteins with marginally hydrophobic signal sequences.


endoplasmic reticulum, membrane protein, protein synthesis, protein translocation, ribosome.

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Copyright © 2021 The Authors. This is an open access article under the CC BY license (

DOI of Published Version



Yi JK, Fujita H, Mandon EC, Gilmore R. Rapid inactivation of the yeast Sec complex selectively blocks transport of post-translationally translocated proteins. J Biol Chem. 2021 Oct;297(4):101171. doi: 10.1016/j.jbc.2021.101171. Epub 2021 Sep 4. PMID: 34492269; PMCID: PMC8503631. Link to article on publisher's site

Journal/Book/Conference Title

The Journal of biological chemistry

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Creative Commons Attribution 4.0 License
This work is licensed under a Creative Commons Attribution 4.0 License.