Human, yeast and hybrid 3-phosphoglycerate kinase gene expression in yeast

When the gene for yeast 3-phosphoglycerate kinase (PGK) is present on a high copy number plasmid in Saccharomyces cerevisiae, 30-40 percent of yeast protein is produced as PGK. However, when the structural part of this gene is replaced by as many as twenty different heterologous genes, production of gene products is greatly reduced--usually by more than 20 fold. This decrease in protein production is accompanied by large decreases in the steady-state levels of mRNA. However, in contrast to these coding sequences, replacement of the yeast PGK structural gene with a human PGK cDNA has little effect on the steady-state mRNA level in yeast. PGK is a two-domain enzyme and its 3-dimensional structure is highly conserved among species. These observations and others have led us to propose that the PGK protein itself might influence its own mRNA levels (Chen et al., Nucleic Acids Res. 12, pp. 8951-8969, 1984). In addition, data is presented here which suggest that the human PGK mRNA is less efficiently translated than the yeast PGK mRNA. Two different mechanisms of controlling gene expression are indicated. Both mechanisms appear to be independent of gene copy number.