The Schizosaccharomyces pombe Homologue of the Chaperone Calnexin Is Essential for Viability (*)
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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.
Footnotes
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↵* This work was supported by research grants from the Medical Research Council of Canada and Faculté de Médecine, Université de Montréal (to L. A. R.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore by hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
The nucleotide sequence(s) reported in this paper has been submitted to the GenBank™/EMBL Data Bank with accession number(s) U13389[GenBank].
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↵1 The abbreviations used are:
- ER
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endoplasmic reticulum
- PAGE
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polyacrylamide gel electrophoresis
- kb
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kilobase(s)
- bp
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base pair(s)
- ORF
-
open reading frame
- aa
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amino acid(s).
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↵2A. M. Carr, personal communication.
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↵3F. Lacroute, unpublished results.
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- Received August 17, 1994.
- Revision received October 18, 1994.
