http://www.jbc.org/content/257/6/3026.full.pdf

Codon selection in yeast.

The biogenesis of mitochondria involves a close interaction between the nucleocytoplasmic and the mitochondrial genetic system. The majority of the mitochondrial proteins are synthesized on cytoplasmic ribosomes and transported into the organelle (1). The mechanism of this protein import has been under debate for many years (e.g., (2,3)). Recent experiments with yeast cells have shown that several cytoplasmic- ally made mitochondrial proteins are initially made as larger precursors, both in vitro as well as in pulse-labeled yeast spheroplasts (4,5). So far, larger precursors have been detected for the following cytoplasmically made mitochondrial proteins: the three largest subunits of the mitochondrial F1-ATPase (i.e., the α, β, and γ subunit, see (4)) and two subunits of the mitochondrial cytochrome bc1 complex (cytochrome c1 and subunit V; (5) and C. Cote, unpublished). Import of in vitro synthesized precursors into isolated mitochondria was demonstrated for the three largest F1-ATPase subunits; as an operational measure of import, we checked whether any of the polypeptides added to the mitochondria became resistant to externally added proteases (4).

https://www.jstor.org/stable/pdfplus/2396657.pdf

Import of proteins into mitochondria.

Sequence of the gene for iso-l-cytochrome c in saccharomyces cerevisiae

https://mmbr.asm.org/content/mmbr/47/3/313.full.pdf

Mechanisms of protein localization.

The coding sequences of genes in the yeast Saccharomyces cerevisiae show a preference for 25 of the 61 possible coding triplets. The degree of this biased codon usage in each gene is positively correlated to its expression level. Highly expressed genes use these 25 major codons almost exclusively. As an experimental approach to studying biased codon usage and its possible role in modulating gene expression, systematic codon replacements were carried out in the highly expressed PGK1 gene. The expression of phosphoglycerate kinase (PGK) was studied both on a high-copy-number plasmid and as a single copy gene integrated into the chromosome. Replacing an increasing number (up to 39% of all codons) of major codons with synonymous minor ones at the 5' end of the coding sequence caused a dramatic decline of the expression level. The PGK protein levels dropped 10-fold. The steady-state mRNA levels also declined, but to a lesser extent (threefold). Our data indicate that this reduction in mRNA levels was due to destabilization caused by impaired translation elongation at the minor codons. By preventing translation of the PGK mRNAs by the introduction of a stop codon 3' and adjacent to the start codon, the steady-state mRNA levels decreased dramatically. We conclude that efficient mRNA translation is required for maintaining mRNA stability in S. cerevisiae. These findings have important implications for the study of the expression of heterologous genes in yeast cells.

B D Hall

Papers

Yeast cytochrome c messenger RNA. In vitro translation and specific immunoprecipitation of the CYC1 gene product.