That a high percentage of human genes have yeast analogues has been known for a long time; some of the genes are very similar, some have mutated to a considerable degree. The degree of similarity didn’t affect the genes’ ability to perform in their strange setting. That, too, doesn’t surprise the experts because genes and the proteins they code for can mutate considerably whilst still retaining their functions.
How is all this possible? Nick Lane has written: “I challenge you to look at one of your own cells down a microscope and distinguish it from the cells of a mushroom”. Mushrooms, yeast (both fungi) and human beings all belong to the same category of creation: the Eukaryotes. Although yeast is single-celled, it already contains many of the genes used to construct multi-cellular creatures. The basic machinery of cellular life was evolved by bacteria long before the eukaryotes evolved and this hasn’t changed very much.
The human genes that work in yeast are these basic metabolic genes. Of course the experiment wouldn’t work in reverse but the important point about the experiment is that it helps us to understand what genes are and what they are not. Genes act in concert so there is rarely a gene “for” a particular trait, as people often imagine. Genes can be co-opted during evolution for different functions in different places, whilst still also continuing with their original function. Genes only really make sense into the context of cells and other genes, so these human genes in yeast don’t really feel so alien because yeast is, after all, a cousin, albeit more than 1 billion years removed.
Science, 22 May 2015, pp. 921-5.