Atypical MAPK protein that regulates protein secretion in a kinase activity-dependent manner (PubMed:21847093, PubMed:25393288). In response to starvation regulates protein secretion by mediating transitional endoplasmic reticulum site disassembly (PubMed:21847093). Mediates inhibition of insulin-like peptide secretion upon disturbed ribosome biogenesis and acts as a downstream effector of TP53 (PubMed:25393288). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Amino-acid starvation stabilizes protein level (PubMed:21847093). Up-regulated upon impaired ribosome biogenesis and starvation (PubMed:25393288). Belongs to the protein kinase superfamily. Ser/Thr protein kinase family.