Figure 2.

Five degrees of yeast humanization. Yeast have proven useful for the direct study of human biology in a variety of forms, illustrated here to distinguish those cases in which yeast were simply studied for human-specific processes and drugs (degree 0), to the heterologous expression of human genes in yeast (degree 1), all the way to the directed replacement of specific amino acids, genes, and pathways (degrees 2–4, respectively). (A colour version of this figure is available online at: http://bfg.oxfordjournals.org)