Yeast as a tool to identify novel protein interactions
Bakers yeast, Saccharomyces cerevisiae, is a unicellular eukaryote which has been widely used as a model system to elucidate many biological processes, such as intracellular signalling, cell cycle control, DNA replication and repair or protein translation.
Its easy genetic manipulation by various means has also made it the choice organism for methods that detect novel protein-protein interactions by means of genetic selection.
Detecting protein-protein interactions in yeast
Protein-protein interactions are intrinsic to virtually every cellular process within a cell and the formation of most cellular structures result from complex interactions between many different proteins. Traditionally, the tools available to analyze protein-protein interactions in multicellular organisms have been restricted to biochemical approaches. However, biochemical approaches can be difficult to set up and time-consuming to carry out.
The identification of protein-protein interactions by means of genetic selection in yeast has several important advantages.
- Researcher's bias is removed: there is no need to manipulate binding or washing conditions, since interactions are detected in vivo.
- Proteins under investigation do not have to be purified and there is no need for cumbersome detection steps after complex purification.
- Novel protein-protein interactions can be easily selected from a pool of potential interaction partners (e.g. a cDNA expression library).
- Genetic screening systems yield not only information on the interaction itself but also directly provide the cDNA encoding the novel interaction partner.
The yeast two-hybrid system
Genetic selection for protein-protein interactions in yeast was first demonstrated by Fields and Song (1989) using a method they termed the yeast two-hybrid system. Since its invention in 1989, it has rapidly become the choice method for identifying novel protein-protein interactions.
The split-ubiquitin system and its adaptations
A wide range of similar screening systems have followed, one of them being the split-ubiquitin assay (Johnsson and Varshavsky, 1994). The split-ubiquitin assay is the basis for other genetic methods, such as the DUALmembrane system and a the DUALhunter system.
