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Gene Review

SUR1  -  mannosylinositol phosphorylceramide...

Saccharomyces cerevisiae S288c

Synonyms: BCL21, CSG1, LPE15, Mannosyl phosphorylinositol ceramide synthase SUR1, YPL057C
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High impact information on SUR1

  • CCC1 was previously identified by complementation of a Ca2+-sensitive (csg1) mutant [1].
  • Thus, Csg2 has several regulatory functions for Csg1 and Csh1, including stability, transport, and gene expression [2].
  • One of the yeast complex sphingolipids, mannosylinositol phosphorylceramide (MIPC), is produced by the redundant inositol phosphorylceramide (IPC) mannosyltransferases Csg1 and Csh1 [2].
  • Regulation of the Transport and Protein Levels of the Inositol Phosphorylceramide Mannosyltransferases Csg1 and Csh1 by the Ca2+-binding Protein Csg2 [2].
  • We also demonstrated that Ca(2+) stimulates IPC-to-MIPC conversion, because of a Csg2-dependent increase in Csg1 levels [2].

Biological context of SUR1

  • Here we show that open reading frame YBR161w, renamed CSH1, is functionally homologous to CSG1 and that deletion of both genes abolishes MIPC and M(IP)2C synthesis without affecting protein mannosylation [3].
  • Loss of Csg1p and Csh1p has no effect on clathrin- or AP-3 adaptor-mediated protein transport from the Golgi to the vacuole [3].
  • Suppression of cls2 was observed even after introduction of a single-copy plasmid harboring BCL21 [4].
  • Analyses using Deltacsg1 and Deltacsh1 cells in the Deltaipt1, Deltasur2, or Deltascs7 genetic background demonstrated that Csh1p has a different substrate specificity from Csg1p [5].
  • This gene displays non-allelic complementation of the Ca(2+)-sensitive phenotype conferred by the csg1 mutation [6].

Anatomical context of SUR1

  • Increased osmolarity of the growth medium increases the Ca2+ tolerance of csg1 and csg2 mutant cells, suggesting that altered cell wall synthesis causes Ca(2+)-induced death [7].
  • Further identification of the glycosylated residues suggests that both Csg1 and Csh1 exhibit membrane topology with their C termini in the cytosol and their mannosyltransferase domains in the lumen [2].

Associations of SUR1 with chemical compounds

  • To confirm this hypothesis, a C. albicans gene homologue for the Saccharomyces cerevisiae SUR1 gene was identified and named MIT1 as it coded for GDP-mannose:inositol-phospho-ceramide mannose transferase [8].
  • To better understand the molecular basis of the Ca(2+)-induced growth defect in IPC-C-overaccumulating cells, we searched for genes whose overexpression restored Ca(2+) tolerance in a mutant lacking the IPC mannosyltransferases Csg1p and Csh1p [9].
  • Csg1p and Csg2p have been shown to be involved in the synthesis of mannosylinositol phosphorylceramide (MIPC) from inositol phosphorylceramide [5].

Physical interactions of SUR1


Regulatory relationships of SUR1

  • Increased expression of CCC2 or increased Cu2+ concentration in the growth medium enhances the Ca2+ tolerance of csg1 mutants, suggesting that accumulation of IPC-C renders csg1 cells Ca2+ sensitive [7].
  • BCL21 suppresses the cls2 disruption mutation, indicating that the multicopy suppression does not require the Cls2p [4].

Other interactions of SUR1

  • Here we demonstrate that SUR1/CSG1 is both genetically and biochemically related to CSG2 [7].
  • Ten mutants were obtained, ranged amongst four complementation groups, named SUR1, SUR2, SUR3 and SUR4 [10].
  • A 93-amino acid stretch of Csg1p shows 29% identity with the alpha-1, 6-mannosyltransferase encoded by OCH1 [7].


  1. The product of HUM1, a novel yeast gene, is required for vacuolar Ca2+/H+ exchange and is related to mammalian Na+/Ca2+ exchangers. Pozos, T.C., Sekler, I., Cyert, M.S. Mol. Cell. Biol. (1996) [Pubmed]
  2. Regulation of the Transport and Protein Levels of the Inositol Phosphorylceramide Mannosyltransferases Csg1 and Csh1 by the Ca2+-binding Protein Csg2. Uemura, S., Kihara, A., Iwaki, S., Inokuchi, J., Igarashi, Y. J. Biol. Chem. (2007) [Pubmed]
  3. Protein sorting in the late Golgi of Saccharomyces cerevisiae does not require mannosylated sphingolipids. Lisman, Q., Pomorski, T., Vogelzangs, C., Urli-Stam, D., de Cocq van Delwijnen, W., Holthuis, J.C. J. Biol. Chem. (2004) [Pubmed]
  4. The CLS2 gene encodes a protein with multiple membrane-spanning domains that is important Ca2+ tolerance in yeast. Takita, Y., Ohya, Y., Anraku, Y. Mol. Gen. Genet. (1995) [Pubmed]
  5. Csg1p and newly identified Csh1p function in mannosylinositol phosphorylceramide synthesis by interacting with Csg2p. Uemura, S., Kihara, A., Inokuchi, J., Igarashi, Y. J. Biol. Chem. (2003) [Pubmed]
  6. Sequence, mapping and disruption of CCC2, a gene that cross-complements the Ca(2+)-sensitive phenotype of csg1 mutants and encodes a P-type ATPase belonging to the Cu(2+)-ATPase subfamily. Fu, D., Beeler, T.J., Dunn, T.M. Yeast (1995) [Pubmed]
  7. 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]
  8. Inactivation of CaMIT1 inhibits Candida albicans phospholipomannan beta-mannosylation, reduces virulence, and alters cell wall protein beta-mannosylation. Mille, C., Janbon, G., Delplace, F., Ibata-Ombetta, S., Gaillardin, C., Strecker, G., Jouault, T., Trinel, P.A., Poulain, D. J. Biol. Chem. (2004) [Pubmed]
  9. HOR7, a multicopy suppressor of the Ca2+-induced growth defect in sphingolipid mannosyltransferase-deficient yeast. Lisman, Q., Urli-Stam, D., Holthuis, J.C. J. Biol. Chem. (2004) [Pubmed]
  10. Yeast mutants affected in viability upon starvation have a modified phospholipid composition. Desfarges, L., Durrens, P., Juguelin, H., Cassagne, C., Bonneu, M., Aigle, M. Yeast (1993) [Pubmed]
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