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SEC62 encodes a putative membrane protein required for protein translocation into the yeast endoplasmic reticulum

R J Deshaies1, R Schekman

  • 1Division of Biochemistry and Molecular Biology, University of California, Berkeley 94720.

The Journal of Cell Biology
|December 1, 1989
PubMed

Insights

Yeast sec62 mutants show defects in protein translocation into the endoplasmic reticulum. This defect is localized to the membrane, not the cytosol, and the SEC62 gene product may span the ER membrane.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Protein Translocation

Background:

  • Yeast sec62 mutant cells exhibit impaired translocation of secretory proteins into the endoplasmic reticulum (ER).
  • This defect is particularly pronounced for alpha-factor precursor (pp alpha F) and preprocarboxypeptidase Y.

Purpose of the Study:

  • To investigate the molecular basis of the sec62 mutant's protein translocation defect.
  • To determine the cellular localization and potential function of the SEC62 gene product.

Main Methods:

  • In vitro translocation assays using membranes and cytosol from wild-type and sec62 mutant yeast cells.
  • DNA sequence analysis of the SEC62 gene to predict the protein's structure and localization.

Main Results:

  • Mutant membranes showed significantly reduced and unstable translocation activity for pp alpha F compared to wild-type membranes.
  • The translocation defect was specific to the membrane fraction, as mutant cytosol supported translocation into wild-type membranes.
  • SEC62 gene product (Sec62p) is predicted to be a 32-kD transmembrane protein with cytoplasmic N- and C-terminal domains.

Conclusions:

  • The sec62 mutation impairs protein translocation at the ER membrane level.
  • Sec62p is likely an integral component of the ER protein translocation machinery, potentially interacting with other complex proteins.

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