Serine/threonine-protein kinase that phosphorylates SNF1, the catalytic subunit of the SNF1 kinase complex. Acts as an activator of the SNF1 kinase complex and controls its nuclear localization upon glucose and nitrogen depletion. Also required for SNF1 kinase activation under other stress conditions like alkaline pH or presence of cadmium. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Associates with the SNF1 kinase complex. Interacts with SNF1 and REG1. The kinase domain is not sufficient by themself for proper function and that the non-conserved N-terminal and C-terminal domains are critical for the biological activity. The C-terminus promotes interaction of ELM1 and TOS3 kinases with SNF1. Autophosphorylated. Present with 752 molecules/cell in log phase SD medium. Belongs to the protein kinase superfamily. Ser/Thr protein kinase family.