SEC11 is required for signal peptide processing and yeast cell growth

Area of Science:

• Molecular Biology
• Cell Biology
• Biochemistry

Background:

• Secretory protein transport in Saccharomyces cerevisiae involves multiple steps, including signal peptide processing.
• Temperature-sensitive secretion mutants (sec) help elucidate these pathways.
• The sec11 mutant exhibits a unique defect in signal peptide cleavage for multiple secretory proteins.

Purpose of the Study:

• To characterize the molecular defect in the sec11 mutant.
• To identify and clone the SEC11 gene.
• To investigate the function of the SEC11 gene product in protein processing.

Main Methods:

• Isolation and characterization of temperature-sensitive Saccharomyces cerevisiae secretion mutants.
• Complementation of the sec11-7 mutation with a DNA fragment.
• Genetic analysis to confirm the cloned fragment contains the SEC11 gene.
• DNA sequencing of the SEC11 gene.
• Biochemical comparison of the predicted Sec11 protein with known signal peptidases.

Main Results:

• sec11 mutant cells accumulate core-glycosylated secretory proteins (invertase, acid phosphatase) with intact signal peptides at the restrictive temperature (37 degrees C).
• Other sec mutants defective in endoplasmic reticulum export do not show this signal peptide processing defect.
• A DNA fragment complementing sec11-7 was cloned and identified as the SEC11 gene.
• A null mutation in SEC11 is lethal.
• SEC11 encodes a predicted 18.8-kD basic protein (Sec11p) with a hydrophobic N-terminus and a potential N-glycosylation site.
• Sec11p shares characteristics (mass, charge) with subunits of canine and hen oviduct signal peptidases.

Conclusions:

• The SEC11 gene product (Sec11p) is essential for signal peptide processing in Saccharomyces cerevisiae.
• Sec11p is likely a component of the signal peptidase complex.
• The findings suggest a conserved mechanism for signal peptide processing across eukaryotes.