Snf1 protein kinase and the repressors Nrg1 and Nrg2 regulate FLO11, haploid invasive growth, and diploid pseudohyphal differentiation

The Snf1 protein kinase of Saccharomyces cerevisiae is important for many cellular responses to glucose limitation, including haploid invasive growth. We show here that Snf1 regulates transcription of FLO11, which encodes a cell surface glycoprotein required for invasive growth. We further show that Nrg1 and Nrg2, two repressor proteins that interact with Sun, function as negative regulators of invasive growth and as repressors of FLO11. We also examined the role of Sun, Nrg1, and Nrg2 in two other Flo11-dependent processes. Mutations affected the initiation of biofilm formation, which is glucose sensitive, but also affected diploid pseudohyphal differentiation, thereby unexpectedly implicating Snf1 in a response to nitrogen limitation. Deletion of the NRG1 and NRG2 genes suppressed the defects of a snf1 mutant in all of these processes. These findings suggest a model in which the Sun kinase positively regulates Flo11-dependent developmental events by antagonizing Nrg-mediated repression of the FLO11 gene.