Serine/threonine protein kinase involved in mRNA surveillance. Recognizes the substrate consensus sequence [ST]-Q. Involved in nonsense-mediated decay (NMD) of mRNAs containing premature stop codons by phosphorylating smg-2. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Component of a post-splicing multiprotein NMD complex. Belongs to the PI3/PI4-kinase family.