Serine/threonine-protein kinase involved in the phosphorylation of the NAD(+)-dependent glutamate dehydrogenase GDH2. When overexpressed, confers hypersensitivity to rapamycin and induces rapid nuclear accumulation of GLN3 to activate the transcription of nitrogen-regulated genes. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Interacts with URE2 and GDH2. Interacts also with the TORC1 kinase complex. Belongs to the protein kinase superfamily. Ser/Thr protein kinase family.