STT3/YGL022W Summary Help

Standard Name STT3 1
Systematic Name YGL022W
Feature Type ORF, Verified
Description Subunit of the oligosaccharyltransferase complex of the ER lumen; complex catalyzes asparagine-linked glycosylation of newly synthesized proteins; forms a subcomplex with Ost3p and Ost4p and is directly involved in catalysis (1, 2, 3, 4 and see Summary Paragraph)
Name Description STaurosporine and Temperature sensitive 5
Chromosomal Location
ChrVII:452404 to 454560 | ORF Map | GBrowse
Gene Ontology Annotations All STT3 GO evidence and references
  View Computational GO annotations for STT3
Molecular Function
Manually curated
Biological Process
Manually curated
Cellular Component
Manually curated
Regulators 9 genes
Classical genetics
reduction of function
Large-scale survey
reduction of function
136 total interaction(s) for 76 unique genes/features.
Physical Interactions
  • Affinity Capture-MS: 18
  • Affinity Capture-RNA: 2
  • Affinity Capture-Western: 29
  • Co-purification: 6
  • PCA: 8
  • Two-hybrid: 1

Genetic Interactions
  • Dosage Rescue: 2
  • Negative Genetic: 60
  • Positive Genetic: 2
  • Synthetic Growth Defect: 2
  • Synthetic Lethality: 6

Expression Summary
Length (a.a.) 718
Molecular Weight (Da) 81,528
Isoelectric Point (pI) 8.1
Phosphorylation PhosphoGRID | PhosphoPep Database
sequence information
ChrVII:452404 to 454560 | ORF Map | GBrowse
Last Update Coordinates: 2011-02-03 | Sequence: 1996-07-31
Subfeature details
Most Recent Updates
Coordinates Sequence
CDS 1..2157 452404..454560 2011-02-03 1996-07-31
Retrieve sequences
Analyze Sequence
S288C only
S288C vs. other species
S288C vs. other strains
External Links All Associated Seq | E.C. | Entrez Gene | Entrez RefSeq Protein | MIPS | Search all NCBI (Entrez) | UniProtKB
Primary SGDIDS000002990

During N-linked glycosylation of proteins, oligosaccharide chains are assembled on the carrier molecule dolichyl pyrophosphate in the following order: 2 molecules of N-acetylglucosamine (GlcNAc), 9 molecules of mannose, and 3 molecules of glucose. These 14-residue oligosaccharide cores are then transferred to asparagine residues on nascent polypeptide chains in the endoplasmic reticulum (ER). As proteins progress through the Golgi apparatus, the oligosaccharide cores are modified by trimming and extension to generate a diverse array of glycosylated proteins (reviewed in 6, 7).

The oligosaccharyl transferase complex (OST complex) (EC transfers 14-sugar branched oligosaccharides from dolichyl pyrophosphate to asparagine residues. The complex contains nine protein subunits: Ost1p, Ost2p, Ost3p, Ost4p, Ost5p, Ost6p, Stt3p, Swp1p, and Wbp1p, all of which are integral membrane proteins of the ER. The OST complex interacts with the Sec61p pore complex (8) involved in protein import into the ER.

Stt3p and Ost4p were co-purified as the seventh and eighth components of the OST complex (3). Stt3p is involved in recognition of the target peptide and/or catalysis (4, 9, 10). STT3 is an essential gene, but conditional mutants have defective glycosylation (1, 4) and oligosaccharide transfer (11). Like ost6 cells, stt3 mutants are defective in cell wall biosynthesis (12, 13).

The name STT3 comes from the staurosporine and temperature sensitive phenotype (5), which is unique among components of the OST complex (14). The "stt" phenotype is only observed in alleles mutated in the hydrophobic N-terminal domain, in particular the first cytosolic loop. Mutations in the highly conserved (4) C-terminal lumenal domain lead to general glycosylation defects and/or death (14). Staurosporine inhibits Pkc1p, so Stt3p may be a target of the protein kinase C pathway (PKC1 is STT1) (14).

STT3 is homologous to the human genes SIMP (OMIM) (15) and ITM1 (OMIM) (16). Mouse Itm1 and S. pombe stt3+ complement stt3 on rich medium (YPD) but not on minimal medium (SD) (17). Arabidopsis thaliana has two STT3 homologs, STT3a and STT3b, with overlapping but nonidentical functions, but only stt3a mutants are defective in glycosylation and neither gene complements S. cerevisiae stt3.

Last updated: 2005-06-27 Contact SGD

References cited on this page View Complete Literature Guide for STT3
1) Yoshida S, et al.  (1995) STT3, a novel essential gene related to the PKC1/STT1 protein kinase pathway, is involved in protein glycosylation in yeast. Gene 164(1):167-72
2) Spirig U, et al.  (1997) The STT3 protein is a component of the yeast oligosaccharyltransferase complex. Mol Gen Genet 256(6):628-37
3) Karaoglu D, et al.  (1997) The highly conserved Stt3 protein is a subunit of the yeast oligosaccharyltransferase and forms a subcomplex with Ost3p and Ost4p. J Biol Chem 272(51):32513-20
4) Yan Q and Lennarz WJ  (2002) Studies on the function of oligosaccharyl transferase subunits. Stt3p is directly involved in the glycosylation process. J Biol Chem 277(49):47692-700
5) Yoshida S, et al.  (1992) Characterization of a staurosporine- and temperature-sensitive mutant, stt1, of Saccharomyces cerevisiae: STT1 is allelic to PKC1. Mol Gen Genet 231(3):337-44
6) Herscovics A and Orlean P  (1993) Glycoprotein biosynthesis in yeast. FASEB J 7(6):540-50
7) Burda P and Aebi M  (1999) The dolichol pathway of N-linked glycosylation. Biochim Biophys Acta 1426(2):239-57
8) Chavan MM, et al.  (2005) Subunits of the translocon interact with components of the oligosaccharyl transferase complex. J Biol Chem 280(24):22917-24
9) Yan Q and Lennarz WJ  (2002) Studies on the function of oligosaccharyl transferase subunits: a glycosylatable photoprobe binds to the luminal domain of Ost1p. Proc Natl Acad Sci U S A 99(25):15994-9
10) Nilsson I, et al.  (2003) Photocross-linking of nascent chains to the STT3 subunit of the oligosaccharyltransferase complex. J Cell Biol 161(4):715-25
11) Zufferey R, et al.  (1995) STT3, a highly conserved protein required for yeast oligosaccharyl transferase activity in vivo. EMBO J 14(20):4949-60
12) Chavan M, et al.  (2003) Genetic, biochemical, and morphological evidence for the involvement of N-glycosylation in biosynthesis of the cell wall beta1,6-glucan of Saccharomyces cerevisiae. Proc Natl Acad Sci U S A 100(26):15381-6
13) Kimura T, et al.  (1999) N-glycosylation is involved in the sensitivity of Saccharomyces cerevisiae to HM-1 killer toxin secreted from Hansenula mrakii IFO 0895. Appl Microbiol Biotechnol 51(2):176-84
14) Chavan M, et al.  (2003) Insight into functional aspects of Stt3p, a subunit of the oligosaccharyl transferase. Evidence for interaction of the N-terminal domain of Stt3p with the protein kinase C cascade. J Biol Chem 278(51):51441-7
15) McBride K, et al.  (2002) The model B6(dom1) minor histocompatibility antigen is encoded by a mouse homolog of the yeast STT3 gene. Immunogenetics 54(8):562-9
16) Hong G, et al.  (1996) Molecular cloning of a highly conserved mouse and human integral membrane protein (Itm1) and genetic mapping to mouse chromosome 9. Genomics 31(3):295-300
17) Yoshida S, et al.  (1999) Schizosaccharomyces pombe stt3+ is a functional homologue of Saccharomyces cerevisiae STT3 which regulates oligosaccharyltransferase activity. Yeast 15(6):497-505