Snf1/AMPK promotes S-phase entrance by controlling CLB5 transcription in budding yeast

The Saccharomyces cerevisiae Snf1 protein kinase has been reported to be required for adaptation to glucose limitation and for growth on non-fermentable carbon sources. Here we present novel findings indicating that Snf1, the key regulator of cellular energy, is also involved in yeast cell cycle control. The lack of Snf1 alpha-catalytic subunit downregulates the growth rate and CLB5 expression, delaying Sld2 phosphorylation and G(1)/S transition, in cells grown in 2%, but not in 5% glucose. A non-phosphorylatable Snf1 rescues the slow growth phenotype, whereas a wild type or a phosphomimetic mutant is required to rescue growth rate and the G(1)/S delay. Using either Snf1 or Swi6 as a bait, a specific interaction of Snf1 with Swi6, the regulatory subunit of MBF, was detected. In conclusion, this report describes a previously unrecognized role for Snf1 in transcriptional modulation of the G(1) to S transition, differing from the reported AMPK role in controlling the G(1)/S transition in multicellular eukaryotes.