Distinct domains within yeast Sec61p involved in post-translational translocation and protein dislocation.
The translocation of secretory polypeptides into and across the membrane of the endoplasmic reticulum (ER) occurs at the translocon, a pore-forming structure that orchestrates the transport and maturation of polypeptides at the ER membrane. Recent data also suggest that misfolded or unassembled polypeptides exit the ER via the translocon for degradation by the cytosolic ubiquitin/proteasome pathway. Sec61p is a highly conserved multispanning membrane protein that constitutes a core component of the translocon. We have found that the essential function of the Saccharomyces cerevisiae Sec61p is retained upon deletion of either of two internal regions that include transmembrane domains 2 and 3, respectively. However, a deletion mutation encompassing both of these domains was found to be nonfunctional. Characterization of yeast mutants expressing the viable deletion alleles of Sec61p has revealed defects in post-translational translocation. In addition, the transmembrane domain 3 deletion mutant is induced for the unfolded protein response and is defective in the dislocation of a misfolded ER protein. These data demonstrate that the various activities of Sec61p can be functionally dissected. In particular, the transmembrane domain 2 region plays a role in post-translational translocation that is required neither for cotranslational translocation nor for protein dislocation.
Wilkinson
B M
BM
School of Biological Sciences, 2.205 Stopford Building, University of Manchester, Oxford Road, Manchester, M13 9PT, United Kingdom.
Tyson
J R
JR
Reid
P J
PJ
Stirling
C J
CJ
D000595:Amino Acid Sequence; D001692:Biological Transport; D004229:Dithiothreitol / Q000494:pharmacology; D004721:Endoplasmic Reticulum; D005656:Fungal Proteins / Q000378:metabolism*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D026901:Membrane Transport Proteins; D008969:Molecular Sequence Data; D009154:Mutation; D010641:Phenotype; D014176:Protein Biosynthesis; D011489:Protein Denaturation; D017510:Protein Folding; D011498:Protein Precursors / Q000378:metabolism*; D000069816:SEC Translocation Channels; D012441:Saccharomyces cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D017384:Sequence Deletion; D014415:Tunicamycin / Q000494:pharmacology
D005656:Fungal Proteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D011498:Protein Precursors; D000069816:SEC Translocation Channels; C499383:SEC61 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D014415:Tunicamycin; D004229:Dithiothreitol