title: The Schizosaccharomyces pombe homologue of the chaperone calnexin is essential for viability.
abstract: We have cloned a Schizosaccharomyces pombe gene, here designated cnx1, encoding the homologue of the endoplasmic reticulum molecular chaperone calnexin. Disruption of the cnx1 gene was lethal, demonstrating that it has an essential cellular function. Transcription of cnx1 mRNA is initiated at multiple sites, and it can be induced by various stress treatments that lead to the accumulation of unfolded and/or misfolded proteins in the endoplasmic reticulum. The encoded Cnx1p protein more closely resembles its plant and animal calnexin homologues than that of Saccharomyces cerevisiae. Cnx1p is acidic and migrates aberrantly on SDS-polyacrylamide gel electrophoresis, similar to its mammalian counterparts. Cnx1p contains the hallmark KPEDWD motifs that are found in all members of the calnexin/calreticulin family of proteins. Using an in vitro translation-processing system, we have shown that Cnx1p has the characteristic type I topology of calnexin proteins. Unlike its higher eukaryotic homologues, Cnx1p has a site for N-glycosylation that was modified in an in vitro translation-processing assay.
authors.affiliation: Département de biochimie, Université de Montréal, Québec, Canada.
authors.forename: M
authors.initials: M
authors.lastname: Jannatipour
authors.forename: L A
authors.initials: LA
authors.lastname: Rokeach
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D037281:Calnexin; D018833:Chaperonins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D003001:Cloning, Molecular; D004271:DNA, Fungal; D015966:Gene Expression Regulation, Fungal; D006031:Glycosylation; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D008969:Molecular Sequence Data; D012568:Schizosaccharomyces / Q000235:genetics / Q000502:physiology*; D017386:Sequence Homology, Amino Acid
chemical_list: D002135:Calcium-Binding Proteins; D004271:DNA, Fungal; D008565:Membrane Proteins; D037281:Calnexin; D018833:Chaperonins