Evolutionary Aspects of a Genetic Network: Studying the Lactose/Galactose Regulon of Kluyveromyces lactis

The budding yeast Kluyveromyces lactis has diverged from the Saccharomyces lineage before the whole-genome duplication and its genome sequence reveals lower redundancy of many genes. Moreover, it shows lower preference for fermentative carbon metabolism and a broader substrate spectrum making it a particularly rewarding system for comparative and evolutionary studies of carbon-regulated genetic networks. The lactose/galactose regulon of K. lactis , which is regulated by the prototypic transcription activator Gal4 exemplifies important aspects of network evolution when compared with the model GAL regulon of Saccharomyces cerevisiae. Differences in physiology relate to different subcellular compartmentation of regulatory components and, importantly, to quantitative differences in protein–protein interactions rather than major differences in network architecture. Here, we introduce genetic and biochemical tools to study K. lactis in general and the lactose/galactose regulon in particular. We present methods to quantify relevant protein–protein interactions in that network and to visualize such differences in simple plate assays allowing for genetic approaches in further studies.