The best yeast?

At the Massachusetts Institute of Technology (MIT), there is a famous undergraduate engineering course in which the students are given identical boxes of parts and told to design and build a robot to carry out a single assigned task. Naturally, each student uses the same pieces to devise distinctly different robots. There is more than one way to solve the problem, although the solutions differ in their elegance or efficiency. Biological research is the reverse: taking apart the pieces to see how the design really works. Not surprisingly, the pieces are often closely related, even when the final product looks quite different. Just as in the robots, the same task in living cells can be fulfilled by using similar parts in dissimilar ways. The power of two An intriguing example of this sort of engineering comparison is provided by the budding yeast Saccharomyces cerevisiae and the fission yeast Schizosaccharomyces pombe. `Yeast' is a very general term, rather like `animal', and S. pombe is thought to be such an early offshoot of the standard ascomycete lineage that it has recently been dubbed an `archaeascomycete'. Thus, these two fungi are highly diverged from one another in evolution. Neither of them, it should be noted, is closer to humans than the other. Both yeasts are genetically tractable and an extensive collection of molecular tools is available for their study. S. cerevisiae has a long and distinguished experimental history. It is the first eukaryote to have its genome sequenced and, because its biology is well understood, it has also become a common molecular biology tool - a eukaryotic Escherichia coli. Using S. cerevisiae as a model, scientists have dissected a wide variety of cell-biology problems that range from cell-cycle control to protein trafficking to transcriptional regulation. By contrast, the development of S. pombe as a model system is comparatively recent. It has been used predominantly for studies of cell-cycle control and differentiation, although it is now becoming more popular in other cell-biology investigations. What is to be gained from looking at one problem in two yeasts? The robots built by the engineering students use the same parts in different ways to perform the same task. Similarly, the yeasts have distinct differences in carrying out the same general cellular functions. Such variations might have consequences throughout the cell, affecting more than a single process. We can conclude that, if a problem is solved in the s