Evolution has massively rewired molecular circuits controlling gene expression in yeast, Hao Li and Alexander Johnson of the University of California, San Francisco, and their colleagues showed.
They studied how Saccharomyces cerevisiae, Candida albicans and Kluyveromyces lactis use the regulatory protein Mcm1, which directs the transcription of 4–12% of these three species' genes with the help of various partner proteins. The three yeasts differ radically in the genes that are under the influence of the different Mcm1-partner pairs.
Of hundreds of Mcm1-controlled genes studied, fewer than one-fifth respond to Mcm1 in all three yeasts. The protein has picked up and lost partners as the species diverged, and in C. albicans has gained a new DNA-binding site that may help it thrive in human hosts.