OST3/YOR085W Summary Help

Standard Name OST3 1
Systematic Name YOR085W
Feature Type ORF, Verified
Description Gamma subunit of the oligosaccharyltransferase complex of the ER lumen; complex catalyzes asparagine-linked glycosylation of newly synthesized proteins; Ost3p is important for N-glycosylation of a subset of proteins (1, 2 and see Summary Paragraph)
Name Description OligoSaccharylTransferase 1
Chromosomal Location
ChrXV:482033 to 483085 | ORF Map | GBrowse
Gene Ontology Annotations All OST3 GO evidence and references
  View Computational GO annotations for OST3
Molecular Function
Manually curated
Biological Process
Manually curated
Cellular Component
Manually curated
Regulators 5 genes
Classical genetics
Large-scale survey
420 total interaction(s) for 180 unique genes/features.
Physical Interactions
  • Affinity Capture-MS: 4
  • Affinity Capture-RNA: 3
  • Affinity Capture-Western: 25
  • Co-purification: 9
  • PCA: 13
  • Protein-RNA: 1

Genetic Interactions
  • Dosage Rescue: 4
  • Negative Genetic: 288
  • Phenotypic Enhancement: 6
  • Phenotypic Suppression: 24
  • Positive Genetic: 22
  • Synthetic Growth Defect: 13
  • Synthetic Lethality: 7
  • Synthetic Rescue: 1

Expression Summary
Length (a.a.) 350
Molecular Weight (Da) 39,483
Isoelectric Point (pI) 8.61
Phosphorylation PhosphoGRID | PhosphoPep Database
sequence information
ChrXV:482033 to 483085 | ORF Map | GBrowse
Last Update Coordinates: 2011-02-03 | Sequence: 1996-07-31
Subfeature details
Most Recent Updates
Coordinates Sequence
CDS 1..1053 482033..483085 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 SGDIDS000005611

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 3, 4).

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 (5) involved in protein import into the ER.

Ost3p is the gamma subunit (6) of the OST complex, one of the original six subunits purified (7).

Ost3p is homologous to Ost6p (8), and several lines of evidence indicate that they are alternative members of the OST complex. Both proteins are present in the complex at substoichiometric levels. They interact with the same subset of OST complex proteins, and are not co-immunoprecipitated (9). Disruption of either OST3 or OST6 causes only a minor defect in N-glycosylation (1), but deletion of both causes severe underglycosylation of soluble and membrane-bound glycoproteins and a defect in OST complex formation, although this does not result in a growth defect (8).

Although Ost3p and Ost6p share low sequence identity, they have very similar hydropathy profiles (8). They are homologous to the human tumor suppressor N33 (OMIM) (8). One difference between them: ost6 mutants are sensitive to caffeine, SDS, and Calcofluor White--indicating a possible defect in cell wall biogenesis--while ost3 mutants are not (8).

Last updated: 2005-06-27 Contact SGD

References cited on this page View Complete Literature Guide for OST3
1) Karaoglu D, et al.  (1995) Functional characterization of Ost3p. Loss of the 34-kD subunit of the Saccharomyces cerevisiae oligosaccharyltransferase results in biased underglycosylation of acceptor substrates. J Cell Biol 130(3):567-77
2) Knauer R and Lehle L  (1999) The oligosaccharyltransferase complex from yeast. Biochim Biophys Acta 1426(2):259-73
3) Herscovics A and Orlean P  (1993) Glycoprotein biosynthesis in yeast. FASEB J 7(6):540-50
4) Burda P and Aebi M  (1999) The dolichol pathway of N-linked glycosylation. Biochim Biophys Acta 1426(2):239-57
5) Chavan MM, et al.  (2005) Subunits of the translocon interact with components of the oligosaccharyl transferase complex. J Biol Chem 280(24):22917-24
6) Knauer R and Lehle L  (1994) The N-oligosaccharyltransferase complex from yeast. FEBS Lett 344(1):83-6
7) Kelleher DJ and Gilmore R  (1994) The Saccharomyces cerevisiae oligosaccharyltransferase is a protein complex composed of Wbp1p, Swp1p, and four additional polypeptides. J Biol Chem 269(17):12908-17
8) Knauer R and Lehle L  (1999) The oligosaccharyltransferase complex from Saccharomyces cerevisiae. Isolation of the OST6 gene, its synthetic interaction with OST3, and analysis of the native complex. J Biol Chem 274(24):17249-56
9) Yan A, et al.  (2003) New findings on interactions among the yeast oligosaccharyl transferase subunits using a chemical cross-linker. J Biol Chem 278(35):33078-87