Upstream S/T kinase for the SNF1 complex; primary SNF1-activating kinase (SAK) that phosphorylates the activation-loop (T210) in low glucose; partially redundant with Elm1p and Tos3p; phosphorylation by Snf1p limits maximal phosphorylation and nuclear entry of Snf1p in low glucose; involved in nitrogen signaling upstream of Snf1p during pseudohyphal growth; family members have functional orthology with LKB1, a mammalian kinase associated with Peutz-Jeghers cancer-susceptibility syndrome