LHS1 and SIL1 provide a lumenal function that is essential for protein translocation into the endoplasmic reticulum.
Lhs1p is an Hsp70-related chaperone localized in the endoplasmic reticulum (ER) lumen. Deltalhs1 mutant cells are viable but are constitutively induced for the unfolded protein response (UPR). Here, we demonstrate a severe growth defect in Deltaire1Deltalhs1 double mutant cells in which the UPR can no longer be induced. In addition, we have identified a UPR- regulated gene, SIL1, whose overexpression is sufficient to suppress the Deltaire1Deltalhs1 growth defect. SIL1 encodes an ER-localized protein that interacts directly with the ATPase domain of Kar2p (BiP), suggesting some role in modulating the activity of this vital chaperone. SIL1 is a non-essential gene but the Deltalhs1Deltasil1 double mutation is lethal and correlates with a complete block of protein translocation into the ER. We conclude that the IRE1-dependent induction of SIL1 is a vital adaptation in Deltalhs1 cells, and that the activities associated with the Lhs1 and Sil1 proteins constitute an essential function required for protein translocation into the ER. The Sil1 protein appears widespread amongst eukaryotes, with homologues in Yarrowia lipolytica (Sls1p), Drosophila and mammals.
Tyson
J R
JR
School of Biological Sciences, 2.205 Stopford Building, University of Manchester, Oxford Road, Manchester M13 9PT, UK.
Stirling
C J
CJ
D000251:Adenosine Triphosphatases / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001426:Bacterial Proteins / Q000235:genetics / Q000502:physiology*; D002352:Carrier Proteins / Q000502:physiology*; D002455:Cell Division; D004330:Drosophila / Q000737:chemistry; D004591:Electrophoresis, Polyacrylamide Gel; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D017930:Genes, Reporter; D005978:Glutathione / Q000378:metabolism; D005982:Glutathione Transferase / Q000378:metabolism; D020662:Guanine Nucleotide Exchange Factors; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D006801:Humans; D015151:Immunoblotting; D026901:Membrane Transport Proteins; D018832:Molecular Chaperones; D008969:Molecular Sequence Data; D009154:Mutation; D010957:Plasmids / Q000378:metabolism; D011233:Precipitin Tests; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins; D012685:Sepharose / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013489:Suppression, Genetic; D013997:Time Factors; D014415:Tunicamycin / Q000494:pharmacology; D001616:beta-Galactosidase / Q000378:metabolism
D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D002352:Carrier Proteins; D020662:Guanine Nucleotide Exchange Factors; D018840:HSP70 Heat-Shock Proteins; C102115:LHS1 protein, S cerevisiae; D026901:Membrane Transport Proteins; D018832:Molecular Chaperones; D011993:Recombinant Fusion Proteins; C513385:SIL1 protein, S cerevisiae; C418483:SIL1 protein, human; D029701:Saccharomyces cerevisiae Proteins; D014415:Tunicamycin; D012685:Sepharose; D005982:Glutathione Transferase; D001616:beta-Galactosidase; D000251:Adenosine Triphosphatases; D005978:Glutathione