Subcellular localization of the Snf1 kinase is regulated by specific β subunits and a novel glucose signaling mechanism

TLDR

The Snf1/AMP‑activated protein kinase family regulates transcriptional, metabolic, and developmental responses to stress, and in yeast Snf1 is essential for adaptation to glucose limitation. The study aims to determine how β subunits control Snf1 subcellular localization and to identify a novel glucose‑phosphorylation signaling pathway that governs this nuclear targeting. Using GFP fusions of the β subunits Gal83, Sip1, and Sip2, the authors examined Snf1 complex composition and mapped the distinct localization patterns, revealing a glucose‑phosphorylation–dependent pathway that directs Snf1 to the nucleus. GFP tagging showed that Gal83, Sip1, and Sip2 localize to nucleus, vacuole, or cytoplasm respectively, with Gal83 directing Snf1 nuclear import in a glucose‑regulated manner; this pathway is separate from the activity‑inhibiting glucose pathway, demonstrating independent regulation of Snf1 localization and activity and providing versatile physiological control.

Abstract

The Snf1/AMP-activated protein kinase family has broad roles in transcriptional, metabolic, and developmental regulation in response to stress. In Saccharomyces cerevisiae , Snf1 is required for the response to glucose limitation. Snf1 kinase complexes contain the α (catalytic) subunit Snf1, one of the three related β subunits Gal83, Sip1, or Sip2, and the γ subunit Snf4. We present evidence that the β subunits regulate the subcellular localization of the Snf1 kinase. Green fluorescent protein fusions to Gal83, Sip1, and Sip2 show different patterns of localization to the nucleus, vacuole, and/or cytoplasm. We show that Gal83 directs Snf1 to the nucleus in a glucose-regulated manner. We further identify a novel signaling pathway that controls this nuclear localization in response to glucose phosphorylation. This pathway is distinct from the glucose signaling pathway that inhibits Snf1 kinase activity and responds not only to glucose but also to galactose and sucrose. Such independent regulation of the localization and the activity of the Snf1 kinase, combined with the distinct localization of kinases containing different β subunits, affords versatility in regulating physiological responses.