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Catalytic Activity
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Dolichyl diphosphooligosaccharide + [protein]- L-asparagine = dolichyl diphosphate + a glycoprotein with the oligosaccharide chain attached by N-beta-D-glycosyl linkage to a protein L-asparagine.
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Function
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Essential subunit of the N-oligosaccharyl transferase (OST) complex which catalyzes the transfer of a high mannose oligosaccharide from a lipid-linked oligosaccharide donor to an asparagine residue within an Asn-X-Ser/Thr consensus motif in nascent polypeptide chains. N-glycosylation occurs cotranslationally and the complex associates with the Sec61 complex at the channel-forming translocon complex that mediates protein translocation across the endoplasmic reticulum (ER). All subunits are required for a maximal enzyme activity. OST4 is required for recruitment of OST3 or OST6 to the OST complex. It is essential for cell growth at 37 but not at 25 degrees Celsius.
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Interaction
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P48439:OST3; NbExp=2; IntAct=EBI-12689, EBI-12680; P52870:SBH1; NbExp=2; IntAct=EBI-12689, EBI-16410; P32915:SEC61; NbExp=2; IntAct=EBI-12689, EBI-16400; P35179:SSS1; NbExp=2; IntAct=EBI-12689, EBI-16406;
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Miscellaneous
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Present with 2430 molecules/cell in log phase SD medium
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Miscellaneous
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Present with 2430 molecules/cell in log phase SD medium. {ECO:0000269|PubMed:14562106}.
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Pathway
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Protein modification; protein glycosylation.
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Similarity
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Belongs to the OST4 family
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Similarity
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Belongs to the OST4 family. {ECO:0000305}.
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Subcellular Location
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Endoplasmic reticulum membrane; Single-pass type III membrane protein.
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Subunit
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Component of the oligosaccharyltransferase (OST) complex, which appears to exist in two assemblies comprising OST1, OST2, OST4, OST5, STT3, SWP1, WPB1, and either OST3 or OST6. OST3, OST4 and STT3 probably form a subcomplex. May interact directly with OST2, OST3, OST5, OST6, STT3, WBP1 and SWP1. Interacts with SEC61, SBH1 and SSS1. {ECO:0000269|PubMed:10677492, ECO:0000269|PubMed:15831493, ECO:0000269|PubMed:15886282, ECO:0000269|PubMed:8175708, ECO:0000269|PubMed:9405463}.
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