Functions in the let-60 Ras signaling pathway; acts downstream of lin-45 raf kinase, but before the sur-1/mpk-1 gene product in controlling vulval cell differentiation (PubMed:7729690). Required for progression of developing oocytes through the pachytene stage (PubMed:19826475). Plays a role in responses to M.nematophilum-mediated bacterial infection by promoting tail swelling and preventing constipation (PubMed:15268855). Involved in fluid homeostasis (PubMed:11689700). Positively regulates lifespan upstream of mpk-1 (PubMed:20624915). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] ATP + L-tyrosyl-[protein] = ADP + H(+) + O-phospho-L-tyrosyl-[protein] Activated by tyrosine and threonine phosphorylation catalyzed by MAP kinase kinase kinases. Interacts with ksr-1. RNAi-mediated knockdown causes a defect in pachytene progression resulting in a proximal gonad devoid of nuclei. The phenotype is more severe in gck-1 km15 mutant background (PubMed:19826475). RNAi-mediated knockdown in adults decreases lifespan (PubMed:20624915). Belongs to the protein kinase superfamily. STE Ser/Thr protein kinase family. MAP kinase kinase subfamily.