Yeast - Introduction/Overview to Saccharomyces cerevisiae


A few basic facts about the baking, brewing, wine-making yeast

Most of us know the yeast Saccharomyces cerevisiae (see figure 1) better as brewers or bakers yeast. In the ensuing 8000 years, this fungus played a central role in food production and conservation thanks to its ability to ferment glucose to ethanol and carbon-dioxide. But not only being useful in daily brewers and bakers practice, yeast, as a simple, unicellular eukaryote developed to a unique powerful model system for biological research. Its prominent useful features are the cheap and easy cultivation, short generation times, the detailed genetic and biochemical knowledge accumulated in many years of research and the ease of the application of molecular techniques for its genetic manipulation. Therefore, this organism provides a highly suitable system to study basic biological processes that are relevant for many other higher eukaryotes including man. After the determination of the complete genomes of two prokaryotes, M. genitalium and H. influencae, the first complete genomic DNA sequence of an eukaryote has been unraveled as a result of a worldwide scientific collaboration. Bioinformatics has helped to assemble the DNA sequence of the sixteen chromosomes and to extract the amino acid sequences of more than 6000 open reading frames (ORFs) with a length of more than 99 amino acids.

Figure 1: Electron microscopic view of the bakers yeast Saccharomyces cerevisiae. The unicellular organism is in the state of budding and thereby reproducing itself.
Inventory overwiew of the yeast genome

The whole Saccharomyces cerevisiae nuclear genome contains 16 chromosomes including more than 13 million bases. As all other eukaryotic organisms the yeast Saccharomyces cerevisiae contains an additional, extranuclear genome in the mitochondria.

The DNA sequences of both the nuclear and the mitochondrial genome were analyzed by MIPS with regard to putative protein-coding Open Reading Frames , RNA genes and some DNA elements. The methods used for th e identification of putative ORFs only identified ORFs larger than 99 amino acids, smaller ORFs have been identified by s imilarity to known proteins or were already known. In the nuclear genome altoge ther 6275 ORFs have been extracted. 87 of them are smaller than 100 amino acid s. The analysis of the mitochondrial genome results in 32 ORFs, of which 4 are smaller than 100 amino acids.