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Gene Review

OCH1  -  Och1p

Saccharomyces cerevisiae S288c

Synonyms: Initiation-specific alpha-1,6-mannosyltransferase, LDB12, NGD29, Outer chain elongation protein 1, YGL038C
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Disease relevance of OCH1

  • A series of influenza virus hemagglutinin (HA) epitope-tagged fusion proteins was constructed in which invertase is appended to the Golgi-luminal carboxy terminus of full-length Och1p [1].

High impact information on OCH1

  • At steady state, de novo-synthesized and TGN-generated HA epitope-tagged Och1p reside in a compartment with a buoyant density identical to that of wild-type Och1p and distinct from that of the vacuole or the TGN [1].
  • The Och1p-Kex2p site-invertase fusion protein is cleaved with a half-time of 5 min, and the process proceeds to completion [1].
  • To analyze the mechanism of integral membrane protein localization in the early Golgi apparatus of Saccharomyces cerevisiae, we have used Och1p, a cis-Golgi mannosyltransferase [1].
  • Finally, och1 null cells that express an Ochlp fusion construct known to rapidly encounter the TGN glycosylate invertase to the same extent as wild-type cells, indicating that they have phenotypically wild-type Och1p activity [1].
  • Subcellular fractionation revealed that > 90% of the alpha 1,6 mannose-modified fusion protein colocalized with the ER (Wbp1p) and not with the Golgi Och1p-containing compartment or other membrane fractions [2].

Biological context of OCH1

  • We have cloned the OCH1 gene by complementation of temperature sensitive (ts) phenotype for growth [3].
  • The OCH1 gene disruptant is not lethal but ts for cell growth, and lacks mannose outer chains [3].
  • Most interestingly, Hpocr1Delta showed a severe defect in the O-linked glycosylation of extracellular chitinase, representing HpOCR1 as a novel member of the OCH1 family implicated in both N- and O-linked glycosylation [4].
  • Our studies reveal that the Skn7p HSF-like DNA binding domain interacts with a cis-acting element identified upstream of OCH1 that is distinct from the previously defined HSE-like Skn7p binding site [5].
  • Cloning, sequencing and disruption of NGD29 showed that it is a non lethal gene and identical to OCH1 [6].

Anatomical context of OCH1

  • Our results suggest that the blocking of vesicle transport by a loss of the Trs130p function causes some defect in the cell wall mannoproteins, which leads to the elevated expression of OCH1 through the Skn7p function, to compensate for the defect [7].
  • The Saccharomyces cerevisiae Och1p is required for the initiation of the mannose outer chain elongation of cell wall mannoproteins [7].
  • In vitro translation/translocation analysis revealed that the large C-terminal region of the OCH1 protein is located at the lumenal side of microsomal membranes with some sugar modification, indicating a type II membrane topology [3].
  • The OCH1 protein was detected in yeast membrane fractions as four forms of 58-66 kDa, which correspond to the size of a glycoprotein containing four N-linked sugar chains the length of which is almost the same or slightly larger than the inner core (Man8GlcNAc2) formed in the endoplasmic reticulum (ER) [3].
  • We find that Och1p does not cycle via endosomes during its normal itinerary suggesting that Och1p engages in intra-Golgi cycling only [8].

Associations of OCH1 with chemical compounds

  • The Saccharomyces cerevisiae OCH1 gene encodes an alpha-1,6-mannosyltransferase that initiates the polymannose outer chain elongation of N-linked glycans [9].
  • OCH1 encodes a novel membrane bound mannosyltransferase: outer chain elongation of asparagine-linked oligosaccharides [3].
  • The eukaryotic two-component histidine kinase Sln1p regulates OCH1 via the transcription factor, Skn7p [5].
  • Man8GlcNAcOH that involves an open sugar ring by reduction of reducing terminal GlcNAc residue did not serve as an acceptor for Och1p [10].
  • These results contrast the far simpler glycan profile found in Saccharomyces cerevisiae alg3-1 och1, indicating diverging Golgi processing in these two closely related yeasts [11].

Other interactions of OCH1

  • A 93-amino acid stretch of Csg1p shows 29% identity with the alpha-1, 6-mannosyltransferase encoded by OCH1 [12].
  • In this study, we attempted to gain an understanding of the relationship between the defect in the Trs130p function and the elevated expression of OCH1 [7].
  • We suggest that transcriptional control of OCH1 by cdc4(bon) is through Swi4, because cdc4(bon) cannot activate the OCH1-lacZ reporter in a strain deleted for SWI4 [9].
  • The HOC1 gene (Homologous to OCH1) is predicted to encode a type II integral membrane protein that strongly resembles Och 1p, an alpha-1,6-mannosyltransferase [13].
  • Subcellular fractionation experiments indicated that the fractionation pattern of Rer1p was similar to that of an early Golgi protein, Och1p [14].

Analytical, diagnostic and therapeutic context of OCH1

  • Mannosyltransferase activity of OCH1 gene product (Och1p) was measured on HPLC by using pyridylaminated Man8GlcNAc2 (Man8GlcNAc2-PA) as an acceptor and the reaction product was observed at the retention time corresponding to Man9GlcNAc2-PA [10].


  1. Localization of a yeast early Golgi mannosyltransferase, Och1p, involves retrograde transport. Harris, S.L., Waters, M.G. J. Cell Biol. (1996) [Pubmed]
  2. Signal-mediated retrieval of a membrane protein from the Golgi to the ER in yeast. Gaynor, E.C., te Heesen, S., Graham, T.R., Aebi, M., Emr, S.D. J. Cell Biol. (1994) [Pubmed]
  3. OCH1 encodes a novel membrane bound mannosyltransferase: outer chain elongation of asparagine-linked oligosaccharides. Nakayama, K., Nagasu, T., Shimma, Y., Kuromitsu, J., Jigami, Y. EMBO J. (1992) [Pubmed]
  4. Functional characterization of the Hansenula polymorpha HOC1, OCH1, and OCR1 genes as members of the yeast OCH1 mannosyltransferase family involved in protein glycosylation. Kim, M.W., Kim, E.J., Kim, J.Y., Park, J.S., Oh, D.B., Shimma, Y., Chiba, Y., Jigami, Y., Rhee, S.K., Kang, H.A. J. Biol. Chem. (2006) [Pubmed]
  5. The eukaryotic two-component histidine kinase Sln1p regulates OCH1 via the transcription factor, Skn7p. Li, S., Dean, S., Li, Z., Horecka, J., Deschenes, R.J., Fassler, J.S. Mol. Biol. Cell (2002) [Pubmed]
  6. Glycoprotein biosynthesis in Saccharomyces cerevisiae: ngd29, an N-glycosylation mutant allelic to och1 having a defect in the initiation of outer chain formation. Lehle, L., Eiden, A., Lehnert, K., Haselbeck, A., Kopetzki, E. FEBS Lett. (1995) [Pubmed]
  7. Mutation of TRS130, which encodes a component of the TRAPP II complex, activates transcription of OCH1 in Saccharomyces cerevisiae. Yamamoto, K., Jigami, Y. Curr. Genet. (2002) [Pubmed]
  8. Retrograde transport of the mannosyltransferase Och1p to the early Golgi requires a component of the COG transport complex. Bruinsma, P., Spelbrink, R.G., Nothwehr, S.F. J. Biol. Chem. (2004) [Pubmed]
  9. Cdc4 is involved in the transcriptional control of OCH1, a gene encoding alpha-1,6-mannosyltransferase in Saccharomyces cerevisiae. Cui, Z., Horecka, J., Jigami, Y. Yeast (2002) [Pubmed]
  10. Substrate specificity of alpha-1,6-mannosyltransferase that initiates N-linked mannose outer chain elongation in Saccharomyces cerevisiae. Nakayama, K., Nakanishi-Shindo, Y., Tanaka, A., Haga-Toda, Y., Jigami, Y. FEBS Lett. (1997) [Pubmed]
  11. Functional analysis of the ALG3 gene encoding the Dol-P-Man: Man5GlcNAc2-PP-Dol mannosyltransferase enzyme of P. pastoris. Davidson, R.C., Nett, J.H., Renfer, E., Li, H., Stadheim, T.A., Miller, B.J., Miele, R.G., Hamilton, S.R., Choi, B.K., Mitchell, T.I., Wildt, S. Glycobiology (2004) [Pubmed]
  12. SUR1 (CSG1/BCL21), a gene necessary for growth of Saccharomyces cerevisiae in the presence of high Ca2+ concentrations at 37 degrees C, is required for mannosylation of inositolphosphorylceramide. Beeler, T.J., Fu, D., Rivera, J., Monaghan, E., Gable, K., Dunn, T.M. Mol. Gen. Genet. (1997) [Pubmed]
  13. Saccharomyces cerevisiae HOC1, a suppressor of pkc1, encodes a putative glycosyltransferase. Neiman, A.M., Mhaiskar, V., Manus, V., Galibert, F., Dean, N. Genetics (1997) [Pubmed]
  14. Membrane protein retrieval from the Golgi apparatus to the endoplasmic reticulum (ER): characterization of the RER1 gene product as a component involved in ER localization of Sec12p. Sato, K., Nishikawa, S., Nakano, A. Mol. Biol. Cell (1995) [Pubmed]
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