The fission yeast Schizosaccharomyces pombe and the budding yeast Saccharomyces cerevisiae have, in addition to being extensively studied themselves, both been utilized for the last quarter century as experimental systems for the isolation of genes from other organisms. Mutations conferring growth defects in either of the two yeast strains have frequently been complemented by expression of cDNA libraries from heterologous species, often human. Many successful experiments have utilized available yeast mutations to allow successful complementation by a human gene, which can thus be deduced to have the same, or an overlapping function as the mutated yeast gene. However complementation in yeast has also been used with success to study two fields, apoptosis and steroid receptor signalling, which, at first glance, seem to be foreign to the yeast life cycle.